Automatic headlights not working

BAKING123

MEMBER
2002 GMC SIERRA
6.0L
V8
4WD
AUTOMATIC
116,000 MILES

If my truck is running, the headlights are on no matter what position the switch is in. If the switch is turned to On, Automatic, or Off, the lights are always on if the engine is running.

If the truck is shut off and the switch is set to Automatic, then the dash lights come on, the headlights are off, and the warning chime is dinging. I replaced the ambient light sensor and the battery, but no change.
I'm guessing the switch, but would like to know how to troubleshoot it first.

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

Yes. More than likely this is the switch. I attached the wiring diagram and the explanation on how the power flow works. Read through the description which looking at the wiring diagram. From here the way to prove it is the switch is to measure voltage in each switch position. Basically you should have voltage at each place that is laid out in the description in each position. If you don't then the switch is the issue.

There is a slight chance that this is a BCM but I highly doubt it. If it were me, I would check voltage and then replace the switch.

Let me know if you have questions and we can go from there.

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