DerekTheGreat
Forum Regular
Came to say what others said about the wiring, check that first. More specifically, there is a harness just under the glove box that burns up and can cause funkiness and perhaps a fire in the worst case scenario. Pull the glove box lid and then the black bin with the RPO sticker on it and that harness will practically be staring you in the eye. I think only the early trucks had it or trucks from 1990-1992. But inspect it for damage/burns and replace/repair as needed. I came across a '92 like that, the HVAC just quit and the display died with it, IIRC. I spliced in a new connector and all was well again.