GM 1978 wiring manual

This

below.

All

booklet

diagrams

contains

contained

INTRODUCTION

Wiring

in

this

Diagrams

booklet

are

for

based

1978

vehicles

on

the

latest

listed

product

in

the

information

1

contents

..

available to

make

VEHICLE

C,

K-10

thru

G-lO P-lO

thru

0-80.

at

the

product

thru

35

35.

• .

time

of

changes

publication at

any

time.

CONTENTS

approval.

The

manufacturer

. . • .

. • • .

CAB,

ENGINE & CHASSIS

WIRING

A-1,

. B-1, 2, 3, 4

C-1,

0-1,

reserves

DIAGRAM

2,

3, 4, 5

2, 3

the

right

•

2

An

electrical source source. conditions:

electricity starts generator. current perly be circuits.

SERIES CIR CUITS

connected way to the

trated PARALLEL connected

of

A

• A

•

• A In

In

source

generator).

path source. vehicle lic

conductor engine. Resistance

switch

ci

rcuit.

order

at

the

returns

operating

classified

series

that

there

follow,

circuit

in

figure

In

parallel

PARALLEL

CIRCUIT

electrical

usable

of

from

The

can

to

have a

must

generator,

It

to

circuits.

as

circuits,

to

other

is only one

as

it

flows

and

1.

CIRCUITS

circuits,

by

parallel

Figure

ELECTRICAL

EQUIPMENT

CIRCUITS

circui t is

energy

circuit

electrical

the

"path"

be a

wire,

such

as

energize

return

is

true,

the

series

each

electrical

from

back

to

a

and

must

energy

source

of a

and/or

as

the

lamps,

and

complete

to

the

it

must

however,

source

Vehicle

circuits,

electrical

devices

path

the

electrical

wires.

path

and

frame,

motors,

de-energize

battery.

even

for

battery

CIRCUIT

+

1 -

Basic

Circuits

from

back

contain

(battery

back

circui

any

ci rcui

return

that

in

circuits

or

device

in

the

as illus-

devices

The

SERIES

CIRCUITRY,

&

PROCEDURES

di

vides;

into

the

to

the

four

or

to

the

t in a

metal-

body

or

etc.

the

t,

the

If

it

to

the

impro-

may

parallel

is

such

current

through

are

current

+

A·6536

a

With switched recei circuits

There cause are Circuit"

OPEN

Whenever interruption as a of

power unit motive

through and an starter

haps to

the

.6...

an

power.

resistance

toms

typical

wil1 resistance An there

pletely

depending

the

proper

Any flow in a tent

An

occur

wiring of within between depending can circuit

SHOR T

The

DIAGNOSTIC

part

of

it

flows

another.

circuits

on and

ves

current

as

CIRCUIT

are

an i

known as an

and a

CIR CUIT

break

itself,

circuit,

the

electrical

solenoid

through

source.

break

"open

In a sense,

will

high

be

no

ammeter

cannot

broken

"open"

use

abnormal

circuit

or

non-functioning.

open

as

the

harness,

electrical

the

easily

condition.

CIRCUIT

term

in

shown

three

noperati

"Grounded

there

in

the

in wiring

to

the

current

wires

and

another

anywhere

circui

appear

on

til

in

the

resistance

heat

because

will

be

(open)

on

where mayor of

meters

resistance

or

result

loose

units,

uni t and

the

create

"short

parallel,

off

independent!

in

figure

MALFUNCTION

electrical

ve ci

"Open

is a

normal

(figure

electrical

will

current

or

cables,

unit

cranking

wire

along

and

the

circuit.

somewhat

created

there

not

current

it

may

is

and

leaves

high-resistance

of a broken

connections

broken

or

poor

ground.

type

and

a

shorted

circui

into

each

by

itself

1.

I'

cui tj

Circuit

Circuit".

complete

current

2)

unit

not

flow. normally

or

units,

to

this

the

complete

break

However,

different

circuit.

is no

register

flow circuit. is

placed

not

give a

covered

reduces

the

ground

location

til

is

one

device,

circuit

since

y of

condi

these

ll

, a

path,

from

throl1gh

motor,

ground

is a high, infini

by

leads

used

the

or

within

In

such

route

That

this current

at

all

through a com-

A

voltmeter,

in

relation

reading.

later.

the

unit

circuit

wire

at

connections

Open

of

or

a

to

part

can

each

the

other

tions condi ti

the

within

that

"Short

break

such

source

an

auto-

travels

switches

as

and

per-

and

back

results

loss

symp- than is,

there

type

flow.

because

current

intermit-

may

terminals

or

wiring

circui the

open

grounded

describe

be

ons

or

the

in

of

te

the

of

to

The

the

ts,

•

"

3

..

T

OPEN

another

which

units. in touching

passes part the tance resul or

insulation nents.

A current conductor causes a conductor is melt smelly the

path

circuit.

GROUNDED

A

ci rcui normal directly wire within a unit or

This condi

sits

tions

as

to the its

type

can

It

refers

the

wrong

each

part

of

the

current

and a higher

ts.

This

component

and

short

severe

wire

housing

of oil,

an ground.

least

circuit

in an

to flow

or

in

two

insulation

melts

so

the

grounded

tin

that

circuit.

to

touching

of

or

terminals,

excellent

back

CIRCUIT PROTECTION

To

protect

CIRCUIT

of

trouble

develop

to a

way,

other,

of

the normal has

found

can

overheat,

of

electrical

through

can

handle.

lasts

and

the

through,

circuit

CIRCUIT

circuit

the

ground.

ground,

coming the

tion

dirt

path

Again,

stance

to

wiring

or in circuit such

so

that

normal.

circuit

the

current

result

course

is

current

In

unit

may

and

ground.

in blown

the

to

heat

long

enough,

insulation

always a sign

there

then

is

this

This

or

in

contact

(figure

also be

moisture

with

these

so

that

current

in

attempting

and

equipment

T

Figure

condi ti on

cal

circui

that

is

as

two

bare

the

current

circuit.

simply

path

burned

inoperative

circuit

conductor

Too

up.

becomes

similar

bypasses

instance,

may

part

2).

the

follows

means

of

least

amperage,

fuses,

causes

much

If

the

will burn.

of

is no

to

be

caused

of

the

with

caused

around

deposits

current

the

to

SHORT

2 -

Circuit

(figure

completed

By-passing

parts

than

overload

wire

trouble.

electrical

an

a

part

by

the

by

connec-

complete

from

2)

ts

or

wires

by- The

that

resis-

flow

wiring

and

compo-

more

the

current

will

Hot,

If

open

short

of

the

going

by a

circui

frame

depo-

acting

flows

path

of

such

CIRCUIT

Malfunctions

overloads, used.

fUSES

circuit or

strip melts circuit

unwanted signed components Naturally, corrected

new

Since amounts are to

correct rati

CIRCUIT

Circui t breakers protector. up a strip and cools, breaker

t

overload

opened

FUSIBLE LINK

A nected system.

smaller

when

ci rcui t

The

before itself

The

tion

mo~t

is a

of

and

interrupts

when

short

to mel t

fuse

will also blow.

different

of

used.

replace

breaking

with

f uses

BREAKERS

bimetallic

moves,

it

remakes

opens and

has

with a switch

fusible

into a heavy

The

than

that

breaker.

function

any

when

fusible

wire

G R 0 U N D E D C I R

circuit

fuse. A fuse

metal,

the

before

a blown

ng.

When a

link is a

circuit

damage

an

protectors

common

inside a glass

there

in

current,

opening

wire the

is

or

before

a

cause

the

are

strip

the

circuit.

the

closes

been

is

circuit

is

of

overload links gauge

the

ground.

circuit

circuits

rated

fuse

circuit

fixed

•

generally

not

the

can

are

size

protector

consists

flow

an

overload

the

wiring

can

must

fuse

is

fuses

its

contact.

short

of in with a fuse

another

overloads,

in

the

contacts

When

until

or

piece

circuit

it

serves,

protected

fusible

occur

develops.

marked

because

CUI

of

some

in

the

of a fine

tube.

of

current

caused

The

fuse

or

be

located

replaced

handle

various

amperes.

form

breaker

temporarily,

the

So

the

cause

the

of

four

gauge

and

by a

link

to

the

on

the

of

T A·6537

type

are

vehicle

wire

The

strip

in

the

by

an

is

de-

electrical

damaged.

and

or

the

different

ratings

Be

sure

of

the

of

ci rcui t

it

heats

and

the

bimetallic

circuit

of

the

circuit

wire

con-

the

wiring

sizes

is

used

fuse

is

to

melt

circuit

insula-

the

heavy

is

or

4

TEST

SUPPLY

LIGHT

t,

Figure

insulation heavier

gauge compartment ble links. insulation fusible

link.

DIAGNOSTIC

The

diagnosis

on

two

thi ngs:

•

The

service definite includes

•

The

diagnosis

ability

given

JUMPER

TEST

(used

12V

3 -

which

than

wire

The

must

step

the

to

by

the

WITH

to

TEST

Diagnostic

makes

it

harnesses

same

size

be used

of

any

ci

technician

by

use of

depends

understand

test

equipment.

WIRE

LIGHT

OWN

check

LIGHT

Procedures

the

actually

POWER

continuity)

link

is.

incorporate

wire

when

with

replacing

EQUIPMENT

rcuit

problem

must step test

procedure

equipment.

on

the

A-6538

appear

a

Engine

fusi-

special

a

is

based

follow a

that

individual's

indications

circuit other unit wire

the

in

by

substituting

wires or

operates

or

switch

leads

figure

CAUTION: A jumper

used to bypass the resistance

3.

of

the

for

when

portion

jumper

the

switches.

jumper

of

wire

a bulb) because the

substitution

the

vehicle

could overload and damage

wiring.

TEST LIGHT

There

•

• The

simply a attached. power from using test parts When one other tion to parallel

circui

operation

longer

The

usually

pencil

bulb, alligator components

are

One

The

type

source.

an

insulated

the

light

of a

lead

the

to

t is

glows

test

obtained

shaped

probe

two

types

requires

other

has

that

12-volt

It

uses

This

wires

as is used in circuit

lead

to

is

moved other, locate

between

and

the

(figure

light

commercially.

unit

and

clip.

It

not

connected

of

outside

its

requires

bulb

the

test

(2

wire

probes

series

in

order

the

lamp

from

the

test

the

open

the

point

3).

with

ground

is used

own

with a pair

vehicle

its

self

source.

COMPASS

jumper

If

the

wire

the

circuit

is

faulty

wire

must

low

test

lights

power.

power

outside

light

type)

to

light

socket

on

the

or

in

check

is

grounded

one

circuit

may

is

circuit.

last

point of

where

own

power

It

cant

lead

fi

primarily

directly

wire

resistance

is used,

between

as

shown

not

be

unit

(i.e.,

resistance

available:

supply.

power

of

wires

battery

be

as a

made

and

other.

parallel

continuity.

and

connec-

being

used in

The

open light

the

light

supply is

consists

ai ned

tted

battery, wi

for

th

testing

to a power

for

the

is

bulb

The

with

the

no

of

an

"..,,Ii

a

•

There

Most

of

are

limited

nosis

procedure.

JUMPER

The

jumper usually end.

The

are

these

to

WIRE

fitted

technician

various

uni ts

one

wire with

types

of

test

have a speci

specific

is

simply a piece

an

can

step

alligator

bypass

equipment.

al

purpose

in

the

clip

at

parts

of

and

diag-

wire

each

of a

An

ordinary

tool

for

use

in compass carrying

In

breaker,

ci

rcuits

makes

current

the

locate a short

use of an

ordinary accomplished following

the

magnetic

locating

use

compass

grounded

of

the

creates a magnetic

that

are

prot

ected

technician

or ground

should quickly

magnetic

by

turni

ng on

wiring

with

is a

circuits.

fact

that a wire

field.

by a ci rcui t

be

through

compass.

the

ci rcui t and

a

compass,

valuable

The

able

to

the

This is

the

5

compass breaker

As the problem trim, fused, manner the

CIRCUIT

By using a a

fuse,

other

A circuit two end

lead.

block fast tion. control clip junction tance, slowed deflection.

AMMETER

closes.

it

passes

compass

can

cover

the

by

fuse.

the

tools

turn

breaker. prongs on cap

from

If

in

to

produce

To slow

rheostat

on a

block.

the

down to

will "kick"

the

will

be

plates

problem

substituting a circuit

BREAKER

circuit

technicIan

to

locate

signal

the

an old

this

unit in

place

of a

it

flasher

good down, in

By

produce

DIAGNOSTIC

each

point

of

the

stop

"kicking".

pinpointed

or

tape.

can

be

located

breaker

can

more

troubles.

flasher

Solder a lead

signal

series

lead,

cutting

rate

makes a convenient

flasher,

fuse

to

inserted

fuse,

it

compass

insert a generator

with

the

of

good

METERS

time

short

without

If

the

as a

substitute

effectively

to

then

the

in

may

needle

the

other

in

additional

the

unit

compass

the

or

ground,

Thus,

removing

circuit

in

the

breaker

each

solder

end

of

the

junction

operate

deflec-

flasher,

clip

may

circui

the

same

for

use

of

the

an

each

too

field

one

in

the

resis-

be

needle

is

t

VOLTMETER

trical unit registers

unit. This because ly, but

meter

through hookup

(parallel)

divides

resistances,

of

from

the

being

allowing

would burn

NOTE:

conduction) ammeter, short vol

tage

connected ber

polarity. connection.

The

in a

type

the

rather

The

Current

the

voltage

Due

if

it

without

to

connect

voltmeter pressure-voltage

circuit.

the

It

therefore of hookup

unlike

voltmeter

parallels

difference

hookup is

the

creates,

ci rcui

flowing

according

voltmeter

circuit

measured.

too

up

to

the

of

the

meter

were

in

Refer

voltage

ammeter,

series

meter

is used

the

ammeter,

is

between

that

and

hooked

some

is is

not

an

t.

through a parallel

to

therefore,

would

and

drop

much

the

across Besides

current

moving

low

resistance

shunt,

in

to

A

drop

it

in

give

located

would

the

terminals

figure

to

drop

voltmeter

also

referred

inserted

existing

directs

while

effect

the

take

act

across a potenti

additional

circuit.

4

measure

of a resistance

through a resistance

pressure

to

covered

into a circuit,

circui

ammeter

all

the

is, an

ratio

internal

an

the

an

through

coil.

between

too

much

untrue

resistance

untrue

(good

within

as a

direct

resistance

Remem-

according

for

correct

the

elec-

senses

sensitive.

as

"paraliel"

previous-

t.

and

volt-

the

current voltmeter additional

circui

resistance

current

reading

reading,

its

circuitry

the

to

and

t

the

of

unit

The

current

to

be

broken

break

circuit, meter

tested. and

the cal meter

second,

current

tion.

posi ti ve

circuit negative

the

circuit.

circuit

The

so

is

will

ammeter

through a conductor.

that

flows

placed

That meter

passing

flows

Care

terminal

and

side.

is used to

and

all

through

in

is,

inserted,

Since

must

pass

indicate

through

must

through

must

the

meter

the

current,

series

the

circuit

all

electrons

through

the

it.

be

it

be

to

the

negative

the

number

taken

measure

The

inserted

in

meter.

with

the

must

thereby

in

the

ammeter,

of

connected

in

the

proper

to

positi

ve

terminal

the

flow

circuit

into

an

electrical

The

circuit

completing

the

amperes

so

connect side

be

that

being

opened

electri-

direc-

of

to

of has the

am-

the per

the

its

the

The current tion, positive circuit negative

so

NOTE:

tance nected being inserted resistance the

nature

and

the value connect ity. tion.

moving

flows

care

terminal

and

side.

Remember,

of

the

in

parallel

tested.

into

unit

of

reading

or

significance.

meter

Refer

coil will

through

must

the

to

be

to

negative

voltmeter,

If

connected

the

circuit

between

the

ci rcui t would

would

terminals figure 4 for

it

taken

the

due

with

operate

in

the

proper

to

positive

terminal

to

the

it

must

the

resistance

in

series,

so

that

the

meter

have

Remember

according

no

correct

only if

direc- connect side

of

to

high

resis-

be

that

there

probes,

be

changed

particular

also

to

polar-

connec-

the

the the

con-

unit

is

its

is, no

to

6

MULTIPLE

RANGE

AMMETER

AMPHERES

VOLTMETER

RESISTANCE

SELECTOR

12

VOLT

BATTERY

I

12

VOLT

BATTERY

t

AMMETER

1

AMPHERES

+

Connected series according

2

Measures

f

low.

3

Used

circuit.

VOLTMETER

Connected

1

parallel

circuit

a

of

polarity.

to

Measures

2

drop:

the between at

its

3

Used

circuit.

IN a

circuit

di

in

circuit

to

polarity.

current

in a closed

in

to

a

or

part

according

voltage

This

fference

in a closed

voltage

two

is

leads.

.."",

TEST

OHMMETER

.....-lII!II--</

V

SWITCH

CLOSED

BATTERY

VARIABLE

RESISTANCE

Figure

4-

Basic

OHMS

Meters

and

Connections

1

Has

of

Z

USED UNIT

from

circuit.

Measures

3

directly

OHMMETER

its

own

power.

ONLY WHEN

IS

DISCONNECTED

its

original

resistance

on

supply

meter.

A·6539

GM 1978 wiring manual

Specifications and Main Features

Frequently Asked Questions

User Manual