Diagnosis Of Rear Side Marker Lamps; Diagnosis Of Running, Park And License Lamps - GMC G Service Manual

8B-4 CHASSIS ELECTRICAL

DIAGNOSIS OF REAR SIDE MARKER LAMPS

PROBLEM
1. Turn signal bulb burned out (front lamp).
One Lamp Won't
Work
2.
3.
1.
Front Or Rear Lamps
Won't Work
2.
1.
All Lamps Won't
Work
2.
3.
4.
PARK AND LICENSE LAMPS
PROBLEM
One Side Not 1.
2.
Working
Both Sides Not 1. Tail lamp fuse blown.
Working
2.
3.
4.
5.
POSSIBLE CAUSE
Side marker bulb burned out.
Loose connection or open in wiring.
Loose connection or open ground circuit.
Multiple bulbs burned out.
Blown fuse.
Loose connection.
Open in wiring.
Defective lamp switch.
DIAGNOSIS OF RUNNING,
POSSIBLE CAUSE
Bulb burned out.
Open connection at the bulb socket or the
ground wire terminal.
Loose connection.
Open wiring.
Multiple bulb burnout.
Defective lamp switch.
CORRECTION
1. Switch turn signals on. If the signal bulb does
not light, replace the bulb. (Bulb filament pro­
vides ground path for marker lamp bulb
through the dark blue or brown wires.)
2. Replace the bulb.
3. Using a test lamp, check the brown wire ter­
minal at the bulb socket. If the test bulb lights,
repair the open ground circuit. If the bulb
does not light, repair the open in the brown
wire circuit.
1. If the associated tail or park lamps do not
operate, check all the connectors in the
brown wire circuit. If the park and turn lamps
are not working, repair the open ground
connections.
2. Replace the burned out bulbs.
1. If the park and tail lamps do not operate,
replace the blown fuse. If the new fuse blows,
check for a short to ground between the fuse
panel and the lamps.
2. Secure the connector to the lamp switch.
3. Check the taillamp fuse with a test lamp. If
the test bulb lights, repair the open wiring
between the fuse and the lamp switch. If not,
repair the open wiring between the fuse and
the battery. (Possible open fusible link.)
4. Check the lamp switch with a test lamp. If the
test bulb lights at the orange wire but not at
the brown wire, replace the light switch.
CORRECTION
1. Replace the bulb.
2. Jumper the bulb base socket connection to
ground. If the bulb lights, repair the open
ground circuit.
1. Replace the fuse. If the new fuse blows, re­
pair the short to ground in the brown wire
circuit between the fuse panel through the
lamp switch to the lamp.
2. Secure the connector at the lamp switch.
3. Using a test lamp, check a circuit on both
sides of the fuse. If the test bulb does not light
on either side, repair the open circuit be­
tween the fuse panel and the battery (possi­
ble open fusible link). If the test bulb lights at
the lamp switch brown wire terminal, repair
the open wiring between the lamp switch and
the lamps.
4. If the test bulb lights at the lamp socket brown
wire terminal, replace the bulb(s).
5. If the test bulb lights at the lamp switch
orange wire but not at the brown wire, re­
place the defective lamp switch.
GMTB-0849-2L