I have a '04 LLY D/A GMC 3500 DRW and I'm installing an Autometer EGT Guage. The instructions that came with the guage say to connect the light in the guage to the fuse labelled "ILLUM" for the instrument panel lights. I can't find any such fuse in any of the fuse boxes or in the GMC manual. Does anyone know which fuse controls the dash lighting that comes on with the headlights?

I could just wire it into a constant power source but would rather have it just come on when needed. Any help very much appreciated. Thanks!:)

I am not sure which fuse will actually allow dimming function but you could tap into the head light switch! Just take a test light and probe into the wire that allows such function. I think I read a post somewhere and the wire was a BRN/???!

What year? ILLUM fuse is correct for several.

I installed mine last weekend and just tapped into the wire behind the light switch. I can't remember the color, but it was one of the ones on the end.

I have a '04 LLY D/A GMC 3500 DRW and I'm installing an Autometer EGT Guage. The instructions that came with the guage say to connect the light in the guage to the fuse labelled "ILLUM" for the instrument panel lights. I can't find any such fuse in any of the fuse boxes or in the GMC manual. Does anyone know which fuse controls the dash lighting that comes on with the headlights?

I could just wire it into a constant power source but would rather have it just come on when needed. Any help very much appreciated. Thanks!:)
You can't find the fuse because it doesn't exisit. 04's (actually I think 03's) and above the dimming signal now comes from the body computer. I had a old trailer pigtail and pulled a couple wires out of the connector and used SL RIDE connector on the relay block. That is the black box down by your left foot. The connector you want is the 3 from the left. Right side, bottom is the dimming signal, middle is ground. I could not find a source for the correct connector. Be careful on tapping in to wires for dimming signals. There two different signals, one for incradesent lamps and one for leds/flouresent displays.

Good Luck,

Jim