The control for the instrument lights changes intensity on its own sometimes. The truck is a 2004 Sierra (4.8) with about 57K.

Is it a rheostat or some other device that controls the lighting intensity?

Any help appreciated.

 

Yes, there's a dial next to the headlight switch, it's part of the headlight switch. You could try pulling the headlight switch out and cleaning the contacts on the rheostat, if you're not afraid to pull the switch apart, or get a new headlight switch. Check the connections at the back of the switch first and make sure that none are loose or broken

 

Thanks Bud,you are always helpful. I'll check that stuff.