GMC 4000 Series Service Manual page 528

GU M U
c
This section, covering maintenance of chassis electrical system
and units, is divided into sub-sections as shown in the Index following:
Section
Miscellaneous E le c t r ic a l...................................................................
Alarm System
Instruments and Gauges
Lighting System
NOTE: Certain electrical units, when closely
associated with other system s or units, are cover­
ed in other sections of this manual as listed below:
Unit
Gauge, Engine Temperature
Gauge, Fuel Tank Unit
Gauge, Vacuum ..................................................
Indicator, Water T e m p e r a tu r e ......................
Motor, Electric Windshield Wiper
Motor, Heater B l o w e r .......................................
Motor, 2-Speed Axle S h i f t ................................
Relay, Blower Control
Speedometer Adapter, 2-Speed Axle
Switch, Air Conditioning C o n t r o l ..................
Switch, Differential Lock
Switch, Engine Overheat
Switch, Heater Blower C o n t r o l ......................
Switch, Low A i r ..................................................
Switch, 2-Speed Axle Shift
Switch, Windshield W i p e r ................................
Tachometer D r i v e ..............................................
W IRING DIAGRAM S
Wiring diagrams, included in applicable "Wir­
ing Diagrams" booklet, show electrical circuits and
connections for standard and optional equipment
used on truck series covered by this manual. Stand­
ard equipment is shown in solid lines on diagrams
and optional equipment is shown in broken lines.
Truck series to which each diagram applies is
shown on each diagram.
W IRING HARNESSES AN D WIRES
Connections between chassis wiring harness
and the engine, body, and lighting wiring harness
are made through a multiple plug and receptacle
G M C S E R V I C E M A N U A L
SECTION 12
.
Sleci^UccU and 9vUi^uune*iti
.....................................................................................
....................................................................
..................................................................................
MISCELLANEOUS ELECTRICAL
Section
......................... 6K
....................................
12
6K
..............
4A
....................................
. . . . 4A
................................ 4A
................................ 6K
5B
............................. 4A
6A
type connector. Connections at instrument clus­
ters, gauges, and units are made through a multiple
plug and receptacle type connector and through
plastic insulated blade-type connectors and screw-
type terminals.
Some wires are grouped and taped together
8
with a moisture and heat resistant black, plastic
type tape to form a wiring harness; in other in­
stances it is more practical to use a single wire
1
or cable. Every wire is of a specific size with
1
plain colored or striped insulation as indicated on
the wiring diagram. Insulation colors assist in
1
tracing circuits and in making proper connections.
In-line and V6 gasoline engine models have a
1
special resistance wire in the engine wiring har­
ness to connect the "IGN" terminal of the ignition
switch to the positive (+) terminal of the ignition
1
coil. The proper length wire is used to provide
correct resistance. This wire is identified on ap­
plicable wiring diagrams as: (20-WHT.-ORN.-&
1
PPL.-CR. TR.) or (20-WHT.-RED & BLK.-CR. TR).
On In-line engine models, the resistance value
of wire is approximately 1.80 ohms, and on V6 en­
gine models, resistance value of the wire is ap­
proximately 1.52 ohms.
During cranking, a full 12-volts is supplied to
coil by shunt wire between starter terminal and
coil terminal.
C O N N E C T O R
TERMINAL
R E M O V IN G T E R M IN A L
Figure 1 — Replacing Blade Type Connector Terminals
Sec. 12
Page 517
Page No.
517
522
522
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TERMINAL LOCK
IN S T A L L IN G T E R M IN A L
T-3323