wiring problem

[tavius]

I have a 1994 c3500 6.5 crew cab with 240,000 on it and I can not turn my headlights on without my ac control display going out, not do my brake lights work. I have checked the fuses and purchased a new headlight switch. One day i got in the truck and this problem occured. What could be causing this?

[HowieE]

tavius
How about some more info? When the AC display lights go out do you still have instrument lights? They should be the same circuit. Do the directional lights work while the headlights are on?

[tavius]

Only some of the instrument lights will come on like the engine check, glow plugs, and battery light, but the back lighting of the instrument panel will not come on at all, nor do my brake lights work with or without the ac display on. My direction lights do work with the headlights on.

[BobND]

Check all your GROUNDS... body to engine grounds, body to frame grounds, etc..