I was trying to hook up my boost and egt guage lights to the light switch dimmer and must have tried the wrong wire.

I'm afraid i shorted something. My headlights work with the auto sensor, but the light switch will not turn my headlights on or off, nor can i turn on my parking lights.
I can dim the cluster lights when the auto sensor kicks on the lights.

I have disconnected my boot and egt guages
I insalled a new headlight switch and that didn't work.

Is there a "headlight control module" or is it the BCM that controls the headlights.

Also it would be great to have the pin outs for the headlight switch so I don't do this again.

2004 GMC 2500HD D/A SLT lb7

Thanks guys

I just did a quick look at the Helms manual and the instrument dimmer control gets a 5 volt reference from the BCM, and sends a portion of it back to the BCM to control the intensity. The output from the BCM that goes to the instrument lamps comes out on BCM connector E-C1. There is a seperate output for dimming LED type indicators on BCM connector B-C1. My guess is that if you tied directly into much of anything on the headlight switch assembly, it wasn't a good thing to do.:(

As for the headlight on signal going from the switch to the BCM, the switch has a ground connection that gets passed through the various switch positions to various inputs to the BCM. The BCM uses its internal reference to one end of a resistor andt the switch signals ground the othe end when selected. The BCM senses the voltage change and acts accordingly.

Looking at the pin-out and functions of the pins on the headlamp switch shows that ALL the pins are low voltage/current lines. There is one 5 volt reference, one ground and the rest are either indicators or signals.

I've never mastered posting pictures on this forum, but if you PM me, I can e-mail drawings.

Bill