GMC 4000 Series Service Manual page 540

N O . 7 N O . 6 N O . 1 D O M ELIG H T
Figure 16— M a in Light Switch
remove from holder. Install new bulb in holder,
p ress inward to lock in place. Insert holder in case
with lugs on holder entering notches in case; then
turn clockwise to lock in place.
DOME LIGHT
On conventional cab models, dome lamp is
mounted on instrument panel and provides lighting
to cab interior, glove box, and across the fuse
block. On tilt cab models, dome light is mounted
at rear of cab above rear window. Dome light on
all vehicles is operated by turning main light
switch knob to extreme counterclockwise position.
BULB REPLACEMENT
Conventional Cab Models
A tubular type bulb is mounted inside glove
box in front of fuse block and is held in position by
two spring-loaded clips. To remove bulb, remove
two screws which attach lens to dash compartment
pillar, then remove lens. Pull bulb forward until
bulb releases from clips. P ress new bulb in until
secure in clips.
Tilt Cab Models (Std. & Conv. Model RPO)
Dome light lens is of molded plastic, with a
lug molded on edge of lens at center top and bot­
tom. To remove lens, grasp lens between thumb
and finger at center, and squeeze sides together to
disengage lugs from assem bly. Bulb used in dome
light is of the tubular type, and is held in position
by two spring-loaded clips (fig. 15). To remove
bulb, pull forward until bulb releases from clips.
Replace bulb and position lens in assembly and
p ress in until lugs snap into place.
M A IN LIGHT SWITCH
Main light switch on instrument panel controls
all lights except the stop light and tell-tale lights.
Light switch assembly is shown in figure 16, and
switch circuit diagram is shown in figure 17.
G M C S E R V I C E M A N U A L
CHASSIS ELECTRICAL A N D INSTRUMENTS
Switch terminals are blade-type. Connector plug,
attached to wiring harness, engages the blade-type
terminals on switch. Connector plug can be install­
ed only in one position. Circuit diagram (fig. 17)
is shown as an aid in checking circuits. A rheostat
is incorporated in the instrument panel light cir­
cuit for purpose of dimming these lights if desired.
breaker built into the switch assembly protects
the headlight and parking light circuits. Before
replacing light switch, make sure trouble is in
switch and not elsewhere in the lighting system
by checking circuits with suitable equipment.
SWITCH REPLACEMENT
Removal
to remove the instrument cluster to gain access
to the light switch.
switch term inals.
then p ress on spring-loaded release button on top
of switch assem bly and pull switch knob and rod
all the way out.
ferrule securing switch to instrument panel, then
remove switch assem bly.
Installation
with locating lug on switch frame engaging hole in
instrument panel. Thread ferrule into switch frame
and tighten firmly, using a wide blade screwdriver.
in until spring-loaded latch engages groove near
end of rod.
switch terminals, pressing it firm ly into place.
The 25-amp automatic reset type circuit
NOTE: On some models, it may be necessary
1. Pull wiring harness connector plug off
2. Pull switch, knob out to extreme position,
3. Use a wide-blade screwdriver to remove
1. Position switch under instrument panel,
2. Insert switch rod through ferrule and push
3. Install wiring harness connector plug on
4o Check operation of all lights.
Sec. 12
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