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Automotive Wiring and Circuit Diagrams

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91 Wiring and Circuit Diagrams Upon completion and review of this chapter, you should be able to: Introduction Today’s vehicles have a vast amount of electrical wiring that, if laid end to end, could stretch for half a mile or more. Today’s technician must be proficient at reading wiring diagrams in order to sort though this great maze of wires. Trying to locate the cause of an electrical problem can be quite difficult if you do not have a good understanding of wiring systems and diagrams. In this chapter, you will learn how wiring harnesses are made, how to read the wiring diagram, how to interpret the symbols used, and how terminals are used. This will reduce the amount of confusion you may experience when repairing an electrical circuit. It is also important to understand how to determine the correct type and size of wire to carry the anticipated amount of current. It is possible to cause an electrical problem by simply using the wrong gauge size of wire. A technician must understand the three factors that cause resistance in a wire—length, diameter, and temperature—to perform repairs correctly. Automotive Wiring Primary wiring is the term used for conductors that carry low voltage. The insulation of pri- mary wires is usually thin. Secondary wiring refers to wires used to carry high voltage, such as ignition spark plug wires. Secondary wires have extra thick insulation. Most of the primary wiring conductors used in the automobile are made of several strands of copper wire wound together and covered with a polyvinyl chloride (PVC) insulation (Figure 4-1). Copper has low resistance and can be connected to easily by using crimping connectors or soldered connections. Other types of conductor materials used in automobiles include silver, gold, aluminum, and tin-plated brass. AUTHOR’S NOTE: Copper is used mainly because of its low cost and availability. Explain when single-stranded or multistranded wire should be used. Explain the use of resistive wires in a circuit. Describe the construction of spark plug wires. Explain how wire size is determined by the American Wire Gauge (AWG) and metric methods. Describe how to determine the correct wire gauge to be used in a circuit. Explain how temperature affects resistance and wire size selection. Explain the purpose and use of printed circuits. Explain why wiring harnesses are used and how they are constructed. Explain the purpose of wiring diagrams. Identify the common electrical symbols that are used. Explain the purpose of the component locator. 91 CHAPTER 4 Primary wiring refers to smaller wire with light insulation. Secondary wiring refers to larger wire or cable with heavier insulation. CM-CH04 6/4/02 2:57 PM Page 91
Transcript
Page 1: Automotive Wiring and Circuit Diagrams

91

Wiring andCircuit DiagramsUpon completion and review of this chapter, you should be able to:

Introduction

Today’s vehicles have a vast amount of electrical wiring that, if laid end to end, could stretch forhalf a mile or more. Today’s technician must be proficient at reading wiring diagrams in order tosort though this great maze of wires. Trying to locate the cause of an electrical problem can bequite difficult if you do not have a good understanding of wiring systems and diagrams.

In this chapter, you will learn how wiring harnesses are made, how to read the wiringdiagram, how to interpret the symbols used, and how terminals are used. This will reducethe amount of confusion you may experience when repairing an electrical circuit. It is alsoimportant to understand how to determine the correct type and size of wire to carry theanticipated amount of current. It is possible to cause an electrical problem by simply usingthe wrong gauge size of wire. A technician must understand the three factors that causeresistance in a wire—length, diameter, and temperature—to perform repairs correctly.

Automotive Wiring

Primary wiring is the term used for conductors that carry low voltage. The insulation of pri-mary wires is usually thin. Secondary wiring refers to wires used to carry high voltage, suchas ignition spark plug wires. Secondary wires have extra thick insulation.

Most of the primary wiring conductors used in the automobile are made of several strandsof copper wire wound together and covered with a polyvinyl chloride (PVC) insulation (Figure4-1). Copper has low resistance and can be connected to easily by using crimping connectors orsoldered connections. Other types of conductor materials used in automobiles include silver,gold, aluminum, and tin-plated brass.

AUTHOR’S NOTE: Copper is used mainly because of its low cost and availability.

Explain when single-stranded ormultistranded wire should be used.

Explain the use of resistive wires in acircuit.

Describe the construction of spark plugwires.

Explain how wire size is determined bythe American Wire Gauge (AWG) andmetric methods.

Describe how to determine the correctwire gauge to be used in a circuit.

Explain how temperature affectsresistance and wire size selection.

Explain the purpose and use of printedcircuits.

Explain why wiring harnesses are usedand how they are constructed.

Explain the purpose of wiring diagrams.

Identify the common electrical symbolsthat are used.

Explain the purpose of the componentlocator.

91

C H A P T E R

4

Primary wiringrefers to smaller wirewith light insulation.

Secondary wiringrefers to larger wireor cable with heavierinsulation.

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92

Stranded wire is used because it is very flexible and has less resistance than solid wire.This is because electrons tend to flow on the outside surface of conductors. Since there is moresurface area exposed in a stranded wire (each strand has its own surface), there is less resis-tance in the stranded wire than in the solid wire (Figure 4-2). The PVC insulation is usedbecause it can withstand temperature extremes and corrosion. PVC insulation is also capable ofwithstanding battery acid, antifreeze, and gasoline. The insulation protects the wire from short-ing to ground and from corrosion.

AUTHOR’S NOTE: General Motors has used single-stranded aluminum wire inlimited applications where no flexing of the wire is expected. For example, it is used

in the taillight circuits.

A ballast resistor is used by some manufacturers to protect the ignition primary circuitfrom excessive voltage. It reduces the current flow through the coil’s primary windings andprovides a stable voltage to the coil. Some automobiles use a resistance wire in the ignitionsystem instead of a ballast resistor. This wire is called the ballast resistor wire and is locatedbetween the ignition switch and the ignition coil (Figure 4-3) in the ignition “RUN” circuit.

Spark plug wires are also resistance wires. The resistance lowers the current flow throughthe wires. By keeping current flow low, the magnetic field created around the wires is kept to

Stranded wiremeans theconductor is madeof several individualwires that arewrapped together.

A ballast resistorreduces the currentflow through theignition coil toincrease the life ofthe coil. Theresistance value ofthe ballast resistor isusually between 0.8and 1.2 ohms.

Resistance wire isdesigned with acertain amount ofresistance per foot.

Spark plug wires areoften referred to astelevision-radio-suppression (TVRS)cables.

PVC insulation

Stranded conductor

Figure 4-1 Stranded primary wire.

Figure 4-2 Stranded wire provides flexibility and more surface area for electron flow than a single-strand solid wire.

Electrons

Conductors

Electrons

Conductor

(A) Stranded wire (B) Single strand wire

CM-CH04 6/4/02 2:57 PM Page 92

Page 3: Automotive Wiring and Circuit Diagrams

a minimum. The magnetic field needs to be controlled because it causes radio interference.The result of this interference is noise on the vehicle’s radio and all nearby radios and televi-sions. The noise can interfere with emergency broadcasts and the radios of emergency vehi-cles. Because of this concern, all ignition systems are designed to minimize radio interference;most do so with resistance-type spark plug wires. Spark plug wires are targeted because theycarry high voltage pulses. The lower current flow has no adverse effect on the firing of thespark plug.

Most spark plug wire conductors are made of nylon, rayon, fiberglass, or aramid threadimpregnated with carbon. This core is surrounded by rubber (Figure 4-4). The carbon-impreg-nated core provides sufficient resistance to reduce RFI, yet does not affect engine operation. Asthe spark plug wires wear because of age and temperature changes, the resistance in the wirewill change. Most plug wires have a resistance value of 3,000 Ω to 6,000 Ω per foot. However,some have between 6,000 Ω and 12,000 Ω. The accepted value when testing is 10,000 Ω perfoot as a general specification.

Because the high voltage within the plug wires can create electromagnetic induction,proper wire routing is important to eliminate the possibility of cross-fire. To prevent cross-fire,the plug wires must be installed in the proper separator. Any two parallel wires next to eachother in the firing order should be positioned as far away from each other as possible (Figure4-5). When induction cross-fire occurs, no spark is jumped from one wire to the other. Thespark is the result of induction from another field. Cross-fire induction is most common in twoparallel wires that fire one after the other in the firing order.

93

Battery Switch

Starting bypass

Ballast(primary resistor)

Coilprimarywinding

Coil secondary winding

Figure 4-3 Ballast resistor used in some ignition primary wiring circuits.

Figure 4-4 Typical spark plug wire.

Cross-fire is theelectromagneticinduction spark thatcan be transmittedin another wire closeto the wire carryingthe current.

Glass and cotton braid

Insulation

Core

Jacket

• silicon – high temperature• hypalon – normal

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94

Wire Sizes

An additional amount of consideration must be given for some margin of safety whenselecting wire size. There are three major factors that determine the proper size of wire to beused:

1. The wire must have a large enough diameter, for the length required, to carry thenecessary current for the load components in the circuit to operate properly.

2. The wire must be able to withstand the anticipated vibration.

3. The wire must be able to withstand the anticipated amount of heat exposure.

Wire size is based on the diameter of the conductor. The larger the diameter, the less theresistance. There are two common size standards used to designate wire size: American WireGauge (AWG) and metric.

The AWG standard assigns a gauge number to the wire based on its diameter. The higherthe number, the smaller the wire diameter. For example, 20-gauge wire is smaller in diameterthan 10-gauge wire. Most electrical systems in the automobile use 14-, 16-, or 18-gauge wire.Some high current circuits will also use 10- or 12-gauge wire. Most battery cables are 2-, 4-, or6-gauge cable.

Both wire diameter and wire length affect resistance. Sixteen-gauge wire is capable ofconducting 20 amperes for 10 feet with minimal voltage drop. However, if the current is to becarried for 15 feet, 14-gauge wire would be required. If 20 amperes were required to be carriedfor 20 feet, then 12-gauge wire would be required. The additional wire size is needed to pre-vent voltage drops in the wire. The illustration (Figure 4-6) lists the wire size required to carrya given amount of current for different lengths.

Another factor to wire resistance is temperature. An increase in temperature creates a sim-ilar increase in resistance. A wire may have a known resistance of 0.03 ohms per 10 feet at70°F. When exposed to temperatures of 170°F, the resistance may increase to 0.04 ohms per 10feet. Wires that are to be installed in areas that experience high temperatures, as in the enginecompartment, must be of a size such that the increased resistance will not affect the operationof the load component. Also, the insulation of the wire must be capable of withstanding thehigh temperatures.

In the metric system, wire size is determined by the cross-sectional area of the wire. Met-ric wire size is expressed in square millimeters (mm2). In this system the smaller the number,the smaller the wire conductor. The approximate equivalent wire size of metric to AWG isshown (Figure 4-7).

Example:firing order1-5-4-2-6-3-7-8

Firing orders andcylinder numberingvary among thedifferent engines

Cable bracket Plug cables7 and 8separatedin cablebracket

Left bankenginecylinders

56 7

8

Figure 4-5 Proper spark plug wire routing to prevent cross-fire. (Reprinted with the permission ofFord Motor Company)

The numberassigned to a wire toindicate its size isreferred to asgauge.

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95

Figure 4-6 The distance the current must be carried is a factor in determining the correct wiregauge to use.

Figure 4-7 Approximate AWG to metric equivalents.

TotalApproximate

CircuitAmperes

12 V

1.01.52345678

1011121518202224304050

100150200

3

1818181818181818181818181818181818181816121010

5

181818181818181818181818181818181816161412108

7

18181818181818181818181818161616161614121088

10

18181818181818181818181818161616161412121086

15

1818181818181818181616161414141212101010644

20

1818181818181818161616161414121212101010644

25

18181818181816161616141412121010101088422

30

18181818161616161614141412121010101088422

40

18181818161616141412121212101010101066421

Wire Gauge (for Length in Feet)

Note: 18 AWG as indicated above this line could be 20 AWG electrically.18 AWG is recommended for mechanical strength.

Metric Size (mm2) AWG (Gauge) Size Ampere Capacity

0.5 20 4 0.8 18 6 1.0 16 8 2.0 14 15 3.0 12 20 5.0 10 30 8.0 8 40 13.0 6 50 19.0 4 60

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Terminals and Connectors

To perform the function of connecting the wires from the voltage source to the load compo-nent reliably, terminal connections are used. Today’s vehicles can have as many as 500 sepa-rate circuit connections. The terminals used to make these connections must be able toperform with very low voltage drop. Terminals are constructed of either brass or steel. Steelterminals usually have a tin or lead coating. A loose or corroded connection can cause anunwanted voltage drop that results in poor operation of the load component. For example, aconnector used in a light circuit that has as little as 10% voltage drop (1.2V) may result in a30% loss of lighting efficiency.

Terminals can be either crimped or soldered to the conductor. The terminal makes theelectrical connection and it must be capable of withstanding the stress of normal vibration. Theillustration (Figure 4-8) shows several different types of terminals used in the automotive elec-trical system. In addition, the following connectors are used on the automobile:

1. Molded connector: These connectors usually have one to four wires that aremolded into a one-piece component (Figure 4-9). Although the connector halvesseparate, the connector itself cannot be taken apart.

2. Multiple-wire hard-shell connector: These connectors usually have a hard plasticshell that holds the connecting terminals of separate wires (Figure 4-10). The wireterminals can be removed from the shell to be repaired.

3. Bulkhead connectors: These connectors are used when several wires must passthrough the bulkhead (Figure 4-11).

4. Weather-Pack Connectors: These connectors have rubber seals on the terminalends and on the covers of the connector half (Figure 4-12). They are used oncomputer circuits to protect the circuit from corrosion, which may result in a voltagedrop.

96

Shop ManualChapter 4, page XX

Shop ManualChapter 4, page XX

Shop ManualChapter 4, page XX

Shop ManualChapter 4, page XX

Ring terminal

Spade terminal

Hook terminal

Butt splice

Three-way “Y” connector

Snap plug terminal

Quick disconnect terminal

Figure 4-8 Primary wire terminals used in automotive applications.

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97

Shop ManualChapter 4, page XX

Figure 4-9 Molded connectors cannot be disassembled to replace damaged terminals.

5. Metri-Pack Connectors: These are like the weather-pack connectors but do nothave the seal on the cover half (Figure 4-13).

6. Heat Shrink Covered Butt Connectors: Recommended for air bag applications bysome manufacturers. Other manufacturers allow NO repairs to the circuitry, while stillothers require silver-soldered connections.

To reduce the number of connectors in the electrical system, a common connectioncan be used (Figure 4-14). If there are several electrical components that are physically close toeach other, a single common connection (splice) eliminates using a separate connector foreach wire.

Printed Circuits

Most instrument panels use printed circuit boards as circuit conductors. A printed circuit ismade of a thin phenolic or fiberglass board that copper (or some other conductive material)has been deposited on. Portions of the conductive metal are then etched or eaten away byacid. The remaining strips of conductors provide the circuit path for the instrument panel illu-mination lights, warning lights, indicator lights, and gauges of the instrument panel (Figure 4-15). The printed circuit board is attached to the back of the instrument panel housing. Anedge connector joins the printed circuit board to the vehicle wiring harness.

Whenever it is necessary to perform repairs on or around the printed circuit board, it isimportant to follow these precautions:

1. When replacing light bulbs, be careful not to cut or tear the surface of the printedcircuit board.

Commonconnections areused to share asource of power or acommon groundand are often calleda splice.

Printed circuitboards are used tosimplify the wiring ofthe circuits theyoperate. Other usesof printed circuitboards include theinside of radios,computers, andsome voltageregulators.

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98

Shoulder

Lockingtab

Latchingleg

Lockingtab

Pincontact

Socketcontact

Bridge

Groove

Wedge

Retainingfinger

Groove

Latchingtongue

WedgeShoulder

Plasticspring

Lockingtang

Latchingtongue

LockingfingerSocketcontact

T-shapedTslots

Lockingfingers

Bladecontact

Latchingtongue

Cut-outnotch

Pincontact

Lockingfinger

Lockingfinger

Cut-outnotch

Socketcontact

Lockingfinger

Fingernotch

Contactfinger

Amp connector

Blade connector

Printed circuit connector

Tang connectorTT

Locking wedge connector

Internal locking finger connector

Figure 4-10 Multiple-wire hard shell connectors.

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99

Figure 4-11 Bulkheadconnector. (Courtesy ofDaimlerChrysler Corporation)

Figure 4-14 Common connections (splices) are used to reduce the amount of wire and connectors.

Figure 4-12 Weather-pack connectoris used to prevent connector corrosion.

Figure 4-13 Metri-packconnector.

Audioalarm

assembly

Brakepressureswitch

Ashtraylight

Cigarettelighter

Instrumentpanel

printed circuit

Lightswitch

HeaterA/C

switchlight

Radio

Clock

G200

0.8

Blk

15

0

0.8

Blk

15

0

0.8

Blk

15

0

0.8

Blk

15

0

0.8

Blk

15

0

0.8

Blk

15

0

0.8

Blk

15

0

0.8

Blk

15

0

0.8 Blk

150

0.8 Blk

150Common ground

Common connections S205

15

0

3 B

lk

C219

2. Do not touch the surface of the printed circuit with your fingers. The acid present innormal body oils can damage the surface.

3. If the printed circuit board needs to be cleaned, use a commercial cleaning solutiondesigned for electrical use. If this solution is not available, it is possible to clean theboard by lightly rubbing the surface with an eraser.

A B I T O F H I S T O R Y

The printed circuit board was developed in 1947 by the British scientist J. A. Sargrove to simplifythe production of radios.

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100

Wiring Harness

Most manufacturers use wiring harnesses to reduce the amount of loose wires hanging underthe hood or dash of an automobile. The wire harness provides for a safe path for the wires ofthe vehicle’s lighting, engine, and accessory components. The wiring harness is made bygrouping insulated wires and wrapping them together. The wires are bundled into separateharness assemblies that are joined together by connector plugs. The multiple-pin connectorplug may have more than 60 individual wire terminals.

There are several complex wiring harnesses in a vehicle, in addition to the simple har-nesses. The engine compartment harness and the under dash harness are examples of complexharnesses (Figure 4-16). Lighting circuits usually use a more simple harness (Figure 4-17). Acomplex harness serves many circuits. The simple harness services only a few circuits. Someindividual circuit wires may branch out of a complex harness to other areas of the vehicle.

Most wiring harnesses now use a flexible conduit to provide for quick wire installation(Figure 4-18). The conduit has a seam that can be opened to accommodate the installation orremoval of wires from the harness. The seam will close once the wires are installed, and willremain closed even if the conduit is bent.

Flexibleprintedcircuit

Gaugeconnector

clips

Fuellevel

dampeningmodule

Bulbassemblies

(16 maximum)

Wiring harnessconnector locations

Fuel leveldampeningmodulelocated hereon optionaltachometercluster

Figure 4-15 Printed circuits eliminate bulky wires behind the instrument panel.

A wire harness isan assembled groupof wires that branchout to the variouselectricalcomponents.

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101

Figure 4-16 Complex wiring harness. (Courtesy of DaimlerChrysler Corporation)

Glove box lamp

To doorTTcourtesyswitch

Stereo wiring

ToTT A/C blowermotor resistor

To right frontTTdoor resistor

Radio wiring

To heater blowerTTmotor resistor

Cigarette lighter

Heater blowermotor feed

Printed circuitboard connectorsAsh tray lamp

To key-in buzzerTTTo key-lampTT

To wiper switchTTTo ignition switch lampTT

To intermittent wipeTTTo turn signal switchTT

To speed control brake wiringTT

To accessory lampsTT

To headlampTTdimmerswitch

To ignitionTTswitch

To stop lamp switchTT

To speed control clutch switchTTTo speed control servoTT

To hatch releaseTT

Bulkhead disconnect

To body wiringTT

To heated rear windowTT

To rear wipe washTT

To left door courtesyTTswitches

To left doorTTspeakers

To stereoTTspeakers MZ24

Fuse block

Lifegate releaseL body M-Z24

Lamp

Ground

Rear wipe and washswitch and lampL body M-Z 44

Heated rear windowswitch and lamp

Headlampswitch

To speed control switch wiringTT

Figure 4-17 Simple wiring harness. (Courtesy ofDaimlerChrysler Corporation)

Figure 4-18 Flexible conduit used to make wiringharnesses.

CM-CH04 6/4/02 2:57 PM Page 101

Page 12: Automotive Wiring and Circuit Diagrams

Wiring Protective Devices

Often overlooked, but very important to the electrical system, are proper wire protectiondevices (Figure 4-19). These devices prevent damage to the wiring by maintaining proper wirerouting and retention. Special clips, retainers, straps, and supplementary insulators provideadditional protection to the conductor over what the insulation itself is capable of providing.Whenever the technician must remove one of these devices to perform a repair, it is importantthat the device be reinstalled to prevent additional electrical problems.

Whenever it is necessary to install additional electrical accessories, try to support the pri-mary wire in at least 1-foot intervals. If the wire must be routed through the frame or body, userubber grommets to protect the wire.

Wiring Diagrams

One of the most important tools for diagnosing and repairing electrical problems is a wiringdiagram. These diagrams identify the wires and connectors from each circuit on a vehicle.They also show where different circuits are interconnected, where they receive their power,where the ground is located, and the colors of the different wires. All of this information iscritical to proper diagnosis of electrical problems. Some wiring diagrams also give additionalinformation that helps you understand how a circuit operates and how to identify certaincomponents (Figure 4-20). Wiring diagrams do not explain how the circuit works; this iswhere your knowledge of electricity comes in handy.

A wiring diagram can show the wiring of the entire vehicle (Figure 4 -21) or a single cir-cuit (Figure 4-22). These single circuit diagrams are also called block diagrams. Wiring dia-grams of the entire vehicle tend to look more complex and threatening than block diagrams.However, once you simplify the diagram to only those wires, connectors, and componentsthat belong to an individual circuit, they become less complex and more valuable.

Wiring diagrams show the wires, connections to switches and other components, andthe type of connector used throughout the circuit. Total vehicle wiring diagrams are normallyspread out over many pages of a service manual. Some are displayed on a single large sheetof paper that folds out of the manual. A system wiring diagram is actually a portion of thetotal vehicle diagram. The system and all related circuitry are shown on a single page. Systemdiagrams are often easier to use than vehicle diagrams simply because there is less informa-tion to sort through.

102

BootTubing

Clip

TYstrap

Tie strap

Sleeve

Retainer

Figure 4-19 Typical wire protection devices. (Courtesy of DaimlerChrysler Corporation)

A wiring diagramis an electricalschematic thatshows a represen-tation of actualelectrical or electroniccomponents (by useof symbols) and thewiring of the vehicle’selectrical systems.

Shop ManualChapter 4, page XX

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103

Figure 4-20 Wiring diagrams provide the technician with necessary information to accurately diagnose the electricalsystems. (Courtesy of DaimlerChrysler Corporation)

Fuses Gives fuse amperageand fuse cavity.

Circuit identification code,circuit code, wire size, and colorcode. “A” shows it‘s a power feed,and it has 14-gauge black wire.You can follow the black wire to…

…a single connector. You seewhat the connector looks like, andnotice it has fusible link wireon the other side of the connector.The connector location is alsoindicated.

The fusible link wire, is a finergauge with a lower melting pointthan the wire it‘s connected to.Here it‘s 20-gauge orangebetween the 14-gauge black and14-gauge pink wires

A splice symbol indicates thejunction of the fusible link with thestandard wire in the circuit.

The bulkhead connector symboltells you the pink wire goes tocavity # 31.

Circuit direction. You are directed to page 47 for the rest of the A-3circuit.

NOTE: THE CONNECTOR CAVITYMAY BE IDENTIFIED ONSOME DIAGRAMS WITH THEOLDER SYSTEM USING “S.C.”(FOR SERVICE CONNECTOR).

This circuit code shows a tracersymbol (*) but not color. Hereyou would look for a 14-gaugepink wire with a tracer which will beblack or white.

Tracer color is indicated. Heretracer is/RD/ 12BK/RD*.

*

T

+

– –

+

T

T

T

J2

T

T

# 36

Fusible link(Hypalon wire)(left side shield-front)

C13 20DB

J2

14D

B

J2 14DB

J2 1

2

J2 14DB

To startersystem(see page 11)

Fuse # 13(5 amp)

J2 14DB# 10

Use cavity # 14(6 amp)circuit breaker o ignition

switch(see page 29)

A2 10GBK

Leftheadlightground(left fendershield-rearof battery)

Black

Battery(front of carleft side)

+ Red

G5

20

DB

Q2

16B

K

J2

14D

B

A1

Grd

A2

6G

BK

J2

14D

B

A3

14B

K

A1

6B

K

To deck lid release(see page 79)

To lift gate release(see page 75)

o rear wash wipe(see page 77)

o speed control(see page 30)

(see page 30.51)

o G5 splice

(Rear ofbattery)

(Rear ofbattery)

A3

20D

B

A3

14P

K

# 31

A3

14P

K

o hazardflasher(see page 471)

A1

8R

D

o heatedrear window(see page 82)

75 Amp

C13

12

BK

/RD

C13

12

BK

/RD

Fusible link(Hypalon wire)(rear of battery)

A1 Grd

A7 6GBK

J2 14DB

A1 Grd

G5

20

DB

Q2

16B

K

**

Remember that electrical circuits need a complete path in order to work. A wiring dia-gram shows the insulated side of the circuit and the point of ground. Also, when lines (orwires) cross on a wiring diagram, this does not mean they connect. If wires are connected,there will be a connector or a dot at the point where they cross. Most wiring diagrams do notshow the location of the wires, connectors, or components in the vehicle. Some have location

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104

V

C13 20OR

C29 18BK

R1 8RD

heater system(see page 33)

To starterTTsystem(see page 11)

R6 14RD

Fusable link(Hypalon wire)(left side shield-front)

C26 20OR

J10 18GY

J1 20OR(left side shield-front)

Fusable link(Hypalon wire)(left side shield-front)

C26 14GY

J10 12PK*

J1 12RD

J1 14PK

R6 12BKR6 18GY

*

T

T

R11

R1

12R

D

*

R6 8BK

J10 12PK

J1 12RD

R6 12BK

# 4

# 37

# 35

(see page 28)

o electronicTTspark advancesystem

o ignition switchTT(see page 29)

To air conditioningTTand heater system(see page 33,34)

R6ToTT Splice

J2 14DBL

J2 14DBL

J2

14D

BL

J2

14D

BL

J214DBL

Note:

This is asplice

Thesepointsdo notconnect

R9

R2 60BK

J2

14D

B

J3

18D

GG

oltageregulator(right sideshield)

(Rear ofbattery)

R3 18OGJ2 14DB

J2 14DBTo low oilTTpressure switch(see page 32)

R9 60BKAir pumpbracketmounting bolt

C9 12BK

J2 14DB

R3 18DG

J2 18DG

To airTTconditioningand

R9

8B

K•

R6

8B

K

(Rear ofbattery)

Generator(right sideforward ofengine)

Component and connectorlocation is giving onwiring diagram.

Wire separated fromcomponent showsconnector orterminal that isconnected to thatcomponent.

Ground symbol indicatesbody or engine groundconnection.

Power feed circuitinformation works bothways–you can trace the

here by going to the pagesindicated, or you may bedirected back to this pointas you check the circuitson pages 11, 13, 14, 28,29, 33 and 34.

This splice symbolindicates that all thesewires are joined to theA1-1 feed circuit splice.

Figure 4-20 (continued)

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105

Figure 4-21 A wiring diagram that covers the complete electrical systems of a vehicle. (Courtesy of American Honda MotorCo., Inc.)

CM-CH04 6/4/02 2:57 PM Page 105

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106

Figure 4-21 (continued)

CM-CH04 6/4/02 2:57 PM Page 106

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107

Figure 4-21 (continued)

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108

Figure 4-21 (continued)

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109

Figure 4-21 (continued)

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110

Figure 4-21 (continued)

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111

Figure 4-21 (continued)

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112

Figure 4-21 (continued)

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113

Figure 4-21 (continued)

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114

Figure 4-22 Wiring diagram illustrating only one specific circuit for easier reference. This is also known as a block diagram.(Courtesy of American Honda Motor Co., Inc.)

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Page 25: Automotive Wiring and Circuit Diagrams

reference numbers displayed by the wires. After studying the wiring diagram, you will knowwhat you are looking for. Then you move to the car to find it.

In addition to entire vehicle and system specific wiring diagrams, there are other dia-grams that may be used to diagnose electricity problems. An electrical schematic shows howthe circuit is connected. It does not show the colors of the wires or their routing. Schematicsare what have been used so far in this book. They display a working model of the circuit.These are especially handy when trying to understand how a circuit works. Schematics aretypically used to show the internal circuitry of a component or to simplify a wiring diagram.One of the troubleshooting techniques used by good electrical technicians is to simplify awiring diagram into a schematic.

Installation diagrams show where and how electrical components and wiring har-nesses are installed in the vehicle. These are helpful when trying to locate where a particularwire or component may be in the car. These diagrams also may show how the component orwiring harness is attached to the vehicle (Figure 4-23).

Electrical Symbols

Most wiring diagrams do not show an actual drawing of the components. Rather they useelectrical symbols to represent the components. Often the symbol displays the basic oper-

Installationdiagrams provide amore accurateduplication of wherethe wire harness,connectors, andcomponents arefound on thevehicle.

In place of actualpictures, a variety ofelectrical symbolsare used to representthe components inthe wiring diagram.

115

Figure 4-23 A typical installation diagram. (Reprinted with the permission of Ford Motor Company)

CM-CH04 6/4/02 2:58 PM Page 115

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A tracer is a thin ordashed line of adifferent color thanthe base color of theinsulation.

116

ation of the component. Many different symbols have been used in wiring diagrams throughthe years. Figure 4-24 shows some of the commonly used symbols. Recently, most manufac-turers have begun to use some new style symbols (Figure 4-25). The reason for the change isbecause most manufacturers are going to electronic media instead of paper forms of servicemanuals. Some of the older symbols are not distinguishable when viewed on a monitor. Youneed to be familiar with all of the symbols; however, you don’t need to memorize all of thevariations. Wiring diagram manuals include a “legend” that helps you interpret the symbols.

A B I T O F H I S T O R Y

The service manuals for early automobiles were hand drawn and labeled. They also had draw-ings of the actual components. As more and more electrical components were added to cars, thisbecame impractical. Soon schematic symbols replaced the component drawings.

Color Codes and Circuit Numbering

Nearly all of the wires in an automobile are covered with colored insulation. These colors areused to identify wires and electrical circuits. The color of the wires is indicated on a wiring dia-gram. Some wiring diagrams also include circuit numbers. These numbers, or letters and num-bers, help identify a specific circuit. Both types of coding makes it easier to diagnose electricalproblems. Unfortunately, not all manufacturers use the same method of wire identification. Figure 4-26 shows common color codes and their abbreviations. Most wiring diagrams listthe appropriate color coding used by the manufacturer. Make sure you understand whatcolor the code is referring to before looking for a wire.

In most color codes, the first group of letters designates the base color of the insulation.If a second group of letters is used, it indicates the color of the tracer. For example, a wiredesignated as WH/BLK would have a white base color with a black tracer.

Ford uses four methods of color coding its wires (Figure 4-27):

1. Solid color.

2. Base color with a stripe (tracer).

3. Base color with hash marks.

4. Base color with dots.

DaimlerChrysler uses a numbering method to designate the circuits on the wiring diagram(Figure 4-28). The circuit identification, wire gauge, and color of the wire are included in thewire number. DaimlerChrysler identifies the main circuits by using a main circuit identificationcode that corresponds to the first letter in the wire number (Figure 4-29).

General Motors uses numbers that include the wire gauge in metric millimeters, the wirecolor, the circuit number, splice number, and ground identification (Figure 4-30). In this exam-ple, the circuit is designated as 100, the wire size is 0.8 mm2, the insulation color is black, thesplice is numbered S114, and the ground is designated as G117.

Most manufacturers also number connectors and terminals for identification.

CM-CH04 6/4/02 2:58 PM Page 116

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117

+–

Ω

Positive

Negative

Ground

Fuse

Circuit breaker

Capacitor

Ohms

Resistor

Series resistor

Coil

Step up coil

Connector

Male connector

Female connector

Multiple connector

Denotes wirecontinues elsewhere

Splice

Splice identification

Optional

Thermal elementbimetal strip

“Y” Windings

Digital readout

Open contact

Closed contact

Closed switch

Open switch

Closed ganged switch

Open ganged switch

Two pole singleTTthrow switch

Pressure switch

Solenoid switch

Mercury switch

Diode or rectifier

–2 2

Wiring withWiring without

gg

Bi directional zener diode

Dual filament lamp

LED light emitting diode

Gauge

Thermistor

Timer

Motor

Armature and brushes

Denotes wire goesthrough grommetDenotes wire goesthrough 40 waydisconnect

Variable resistorVV

Single filament lamp

Timer

M

Denotes wire goes through25 way steering columnconnectorDenotes wire goes through25 way instrument panelconnector

Steeringcolumn

Instrumentpanel

Figure 4-24 Common electrical symbols used in wiring diagrams. (Courtesy of DaimlerChryslerCorporation)

CM-CH04 6/4/02 2:58 PM Page 117

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118

T

G

M

+

16

Electricallyoperated valve

Or

VariableVVresistor

Resistor

Spark plug

Fuse

Light bulbor

or

or

One filament ina multifilamentlight bulb

Heating element

Mechanlcallyoperatedswitch

Meter or gauge

Wire connector,detachable

Semiconductordiode

Electromagneticrelay

Alternator

Motor

Wire junction,detachable

Wire crossing(no connection)

Wire junction,permanent

Battery

Shieldedconductors

Soldered orwelded wiresplice

Wiring crosssection (gauge)

Toggle or rockerTTswitch (manuallyoperated)

Hydraulicallyoperated switch

Solid-staterelay

Thermallyoperated(bimetallic) switch

Manuallyoperated multi-position switch

Solid-statecircuitry

Manuallyoperated switch

Horn

Figure 4-25 Electrical symbols used in more recent manuals.

Figure 4-26 Common color codes used in automotive applications.

AluminumBlackBlue (Dark)BlueBlue (Light)BrownGlazedGrayGreen (Green)Green (Light)MaroonNaturalOrangePinkPurpleRedTanVioletWhiteYellow

ALBLKBLU DKBLUBLU LTBRNGLZGRAGRN DKGRN LTMARNATORNPNKPPLREDTANVLTWHTYEL

BKDBBLBBRGLGRDGLGMNOPKPRRTVWY

BDK BLULLT BLUBN

GDK GRNLT GRN

ORGP

RDTN

WHYL

Color Abbreviations

CM-CH04 6/4/02 2:58 PM Page 118

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119

Figure 4-27 Four methods that Ford uses to color code their wires. (Reprinted with thepermission of Ford Motor Company)

Figure 4-28 DaimlerChrysler’s wiring code identification. (Courtesy of DaimlerChryslerCorporation)

Solid color

Striped

Hashmarked

Dotted

(D) Dot(H) HashmarkStripe is understood

Examples:BK–Solid blackBR–Y – Brown with yellow stripeBK–Y H – Black with yellow hashmarksO–BK D – Orange with black dots

J 2A 18 BL/Y*

Color of wire(Blue with yellow tracer)

Gage of wire(18 Gage)

Part of main circuit(Varies depending on equipment)VV

Main circuit identification

A BATTERY FEED (i.e. Fuselink Feeds,Starter Feeds, Starter Relay)

B BrakesC Climate Control (A/C, Heater, E.B.L.

and Heated Mirror Related Circuits)D Diagnostic CircuitsE Dimming Illumination CircuitsF Fused Circuits (Non-Dedicated Multi-

System Feeds)G Monitoring Circuits (Gages, Clocks,

Warning Devices)H **OPEN**I Not used as a circuit designatorJ **OPEN**K Engine Logic Module Control CircuitsL Exterior Lighting CircuitsM Interior Lighting Circuits (Dome, Courtesy

Lamps, Cargo Lamps)

N ESA Module Electronic CircuitsO Not used as a circuit designatorP Power Options (Battery Feed) (i.e. Seats,

Door Locks, Mirrors, Deck Lid Release,etc.)

Q Power Options (Ignition Feed) (i.e. Win-dows, Power Top, Power Sun Roof, etc.)

R Passive RestraintS Suspension and Steering CircuitsT Transmission/Transaxle, Differential,

Transfer Case and Starter System CircuitsU **OPEN**V Speed Control and Wash Wipe CircuitW **OPEN**X Sound Systems (i.e. Radio and Horn)Y **OPEN**Z Grounds (B)

Main Circuit Identification Codes

Figure 4-29 DaimlerChrysler’s circuit identification codes. (Courtesy of DaimlerChryslerCorporation)

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A componentlocator is used todetermine the exactlocation of several ofthe electricalcomponents.

120

0.8 Blk0.8 Blk

0.8 Blk100

S114

G117

Figure 4-30 GM’s method of circuit and wire identification.

DIN is the abbrevia-tion for DeutscheInstitut füerNormung (GermanInstitute forStandardization) andis the recommendedstandard forEuropeanmanufacturers tofollow.

Standardized Wiring Designations. The Society of Automotive Engineers (SAE) is attemptingto standardize the circuit diagrams used by the various manufacturers. The system that is devel-oped may be similar to the DIN used by import manufacturers. DIN assigns certain color codesto a particular circuit as follows:

Red wires are used for direct battery-powered circuits and also ignition-poweredcircuits.

Black wires are also powered circuits controlled by switches or relays.

Brown wires are usually the grounds.

Green wires are used for ignition primary circuits.

A combination of wire colors is used to identify subcircuits. The base color still identifiesthe circuit’s basic purpose. In addition to standardized color coding, DIN attempts to standard-ize terminal identification and circuit numbering.

Component Locators

The wiring diagrams in most service manuals may not indicate the exact physical location ofthe components of the circuit. In another section of the service manual, or in a separate man-ual, a component locator is provided to help find where a component is installed in thevehicle. The component locator may use both drawings and text to lead the technician to thedesired component (Figure 4-31).

Many electrical components may be hidden behind kick panels, dash boards, fenderwells, and under seats. The use of a component locator will save the technician time in findingthe suspected defective unit.

Summary

Most of the primary wiring conductors used in the automobile are made of several strandsof copper wire wound together and covered with a polyvinyl chloride (PVC) insulation.

Stranded wire is used because of its flexibility and current flows on the surface of theconductors. Because there is more surface area exposed in a stranded wire, there is lessresistance in the stranded wire than in the solid wire.

There are three major factors that determine the proper size of wire to be used: (1) Thewire must be large enough diameter—for the length required—to carry the necessarycurrent for the load components in the circuit to operate properly, (2) The wire must beable to withstand the anticipated vibration, and (3) The wire must be able to withstand theanticipated amount of heat exposure.

Terms to Know

Ballast resistor

Bulkhead connectors

Common connections

Component locator

Cross-fire

DIN

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121

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CM-CH04 6/4/02 2:58 PM Page 121

Page 32: Automotive Wiring and Circuit Diagrams

122

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CM-CH04 6/4/02 2:58 PM Page 122

Page 33: Automotive Wiring and Circuit Diagrams

Wire size is based on the diameter of the conductor.

Factors that affect the resistance of the wire include the conductor material, wire diameter,wire length, and temperature.

Terminals can be either crimped or soldered to the conductor. The terminal makes theelectrical connection and it must be capable of withstanding the stress of normal vibration.

Printed circuit boards are used to simplify the wiring of the circuits they operate. A printedcircuit is made of a thin phenolic or fiberglass board that copper (or some other conductivematerial) has been deposited on.

A wire harness is an assembled group of wires that branch out to the various electricalcomponents. It is used to reduce the amount of loose wires hanging under the hood ordash. It provides for a safe path for the wires of the vehicle’s lighting, engine, andaccessory components.

The wiring harness is made by grouping insulated wires and wrapping them together. Thewires are bundled into separate harness assemblies that are joined together by connectorplugs.

A wiring diagram shows a representation of actual electrical or electronic components andthe wiring of the vehicle’s electrical systems.

The technician’s greatest helpmate in locating electrical problems is the wiring diagram.Correct use of the wiring diagram will reduce the amount of time a technician needs tospend tracing the wires in the vehicle.

In place of actual pictures, a variety of electrical symbols are used to represent thecomponents in the wiring diagram.

Color codes and circuit numbers are used to make tracing wires easier.

In most color codes, the first group of letters designates the base color of the insulation. Ifa second group of letters is used, it indicates the color of the tracer.

A component locator is used to determine the exact location of several of the electricalcomponents.

Review Questions

Short Answer Essays

1. Explain the purpose of wiring diagrams.

2. Explain how wire size is determined by the American Wire Gauge (AWG) and metric methods.

3. Explain the purpose and use of printed circuits.

4. Explain the purpose of the component locator.

5. Explain when single-stranded or multistranded wire should be used.

123

Terms to Know(Continued)

Electrical symbols

Gauge

Installation diagrams

Primary wiring

Printed circuit boards

Resistance wire

Schematic

Secondary wiring

Stranded wire

Tracer

Wire harness

Wiring diagram

CM-CH04 6/4/02 2:58 PM Page 123

Page 34: Automotive Wiring and Circuit Diagrams

124

6. Explain how temperature affects resistance and wire size selection.

7. List the three major factors that determine the proper size of wire to be used.

8. List and describe the different types of terminal connectors used in the automotiveelectrical system.

9. What is the difference between a complex and a simple wiring harness?

10. Describe the methods the three domestic automobile manufacturers use for wiring code identification.

Fill-in-the-Blanks1. There is ___________________ resistance in the stranded wire than in the

solid wire.

2. ___________________ ___________________ is the electromagnetic induction spark thatcan be transmitted in another wire that is close to the wire carryingthe current.

3. Wire size is based on the ___________________ of the conductor.

4. In the AWG standard, the ___________________ the number, the smaller the wire___________________.

5. An increase in temperature creates a ___________________ ___________________ in resistance.

6. ___________________ connectors are used when several wires must pass through the bulkhead.

7. ___________________ ___________________ ___________________ are usedto prevent damage to the wiring by maintaining proper wire routing andretention.

8. A wiring diagram is an electrical schematic that shows a ___________________ of actualelectrical or electronic components (by use of symbols) and the ___________________ ofthe vehicle’s electrical systems.

9. In most color codes, the first group of letters designates the ______________________________________ of the insulation. The second group of letters indicates the color ofthe ___________________.

10. A ___________________ ___________________ is used to determine the exact location ofseveral of the electrical components.

CM-CH04 6/4/02 2:58 PM Page 124

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125

Multiple Choice

1. Automotive wiring is being discussed.Technician A says most primary wiring is made ofseveral strands of copper wire wound together andcovered with an insulation.Technician B says the types of conductor materialsused in automobiles include copper, silver, gold,aluminum, and tin-plated brass.Who is correct?A. A only C. Both A and BB. B only D. Neither A nor B

2. Stranded wire use is being discussed.Technician A says there is less exposed surface areafor electron flow in a stranded wire.Technician B says there is more resistance in thestranded wire than in the same gauge solid wire.Who is correct?A. A only C. Both A and BB. B only D. Neither A nor B

3. Spark plug wires are being discussed.Technician A says RFI is controlled by usingresistances in the conductor of the spark plug wire.Technician B says all late model ignition systems useresistance wires to control RFI.Who is correct?A. A only C. Both A and BB. B only D. Neither A nor B

4. Spark plug wire installation is being discussed.Technician A says there is little that can be done toprevent cross-fire.Technician B says the spark plug wires must beinstalled in the proper separator and any two parallelwires next to each other in the firing order should bepositioned as far away from each other as possible.Who is correct?A. A only C. Both A and BB. B only D. Neither A nor B

5. The selection of the proper size of wire to be used isbeing discussed.Technician A says the wire must be large enough, forthe length required, to carry the amount of currentnecessary for the load components in the circuit tooperate properly.Technician B says temperature has little effect onresistance and it is not a factor in wire size selection.Who is correct?A. A only C. Both A and BB. B only D. Neither A nor B

6. Terminal connectors are being discussed.Technician A says good terminal connections willresist corrosion.Technician B says the terminals can be eithercrimped or soldered to the conductor.Who is correct?A. A only C. Both A and BB. B only D. Neither A nor B

7. Wire routing is being discussed.Technician A says to install additional electricalaccessories it is necessary to support the primary wirein at least 10-foot intervals.Technician B says if the wire must be routed throughthe frame or body, use metal clips to protect the wire.Who is correct?A. A only C. Both A and BB. B only D. Neither A nor B

8. Printed circuit boards are being discussed.Technician A says printed circuit boards are used tosimplify the wiring of the circuits they operate.Technician B says care must be taken not to touchthe board with bare hands.Who is correct?A. A only C. Both A and BB. B only D. Neither A nor B

9. Wiring harnesses are being discussed.Technician A says a wire harness is an assembledgroup of wires that branches out to the variouselectrical components.Technician B says most underhood harnesses aresimple harnesses.Who is correct?A. A only C. Both A and BB. B only D. Neither A nor B

10. Wiring diagrams are being discussed.Technician A says wiring diagrams give the exactlocation of the electrical components.Technician B says a wiring diagram will indicatewhat circuits are interconnected, where circuitsreceive their voltage source, and what color of wiresare used in the circuit.Who is correct?A. A only C. Both A and BB. B only D. Neither A nor B

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CM-CH04 6/4/02 2:58 PM Page 126


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