Automatic headlights not working

2002 GMC SIERRA

116,000 MILES • 6.0L • V8 • 4WD • AUTOMATIC

BAKING123

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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.

Jan 17, 2020 at 4:16 PM

KASEKENNY

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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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Jan 18, 2020 at 10:26 AM