GMC 1976 ZEO 6083 Maintenance Manual page 631

12- 26 CHASSIS ELECTRICAL
ALL HEADLIGHTS DO NOT LIGHT
Head
lights
off
Test light
does not
light
With switch "on",
Test light
touch 12 volt test light
does not light prods from switch's dimmer
switch terminal to ground
Check that harness connector
body is tight on light
switch terminals
" Remove light switch and connector
body from dash panel, if necessary
" Refer to service manual for terminal
location or wire color code . There
are two battery feed terminals
" Touch 12 volt test light prods from
switch's battery feed terminal
(that is not fused) to ground
" Refer to service manual to repair
open in circuit between battery
and switch feed terminal
" If headlights do not light after
this repair, repeat diagnostic
procedure
" Disconnect good light switch immediately
before circuit breaker blade burns.
" Refer to service manual to repair ground in
circuit between light switch and headlights .
" Install good light switch after repair .
" Disconnect good light switch immediately
before circuit breaker blade burns.
" Refer to service manual to repair short or
ground in circuit between light switch
and headlights .
" Install good light switch after repair .
Head
lights
off
Flickering
Test light
does not
light
Insert good light switch
into connector body
Check for headlight
flickering after
one minute operation
Test light
Lights
" Light switch OK
" Repair open in circuit between
dimmer switch and headlights
Touch 12 volt test
light prods between
dimmer switch feed
terminal and ground
Test light
lights
" Light switch OK
" Refer to service manual to repair
open in circuit between light
switch & dimmer switch
No
flickering
Head
lights
on
A-1809
Figure 40-Headlight Switch Diagnosis