Given the metripack connectors are idiot proof, ( thank god for fatigue prone) all the earlier diagrams i have show this "map". The colors change but the routing is the same at least through 98 i know. They got smarter later. Moms duramax shift into R and both mirrors tilt down a few degrees for backing up, way cool, shift out back to where they were. So given aaaallllll the diagrams are this map; the only thing i can see is your switch is wonky, or somebody messed with the mirrors internals, or a wiring fault somewhere. You can very gently take your switch apart. Gently like your newborn baby gently, not like Atom bombs to Hand grenades. I have worked with those kind of problem children. And now my mirrors are sporadically functional. And the swtch is original, so what 26 years. It had good life. So I'm going to Autopsy the old switch for the hellofit. Good luck.