Had a late 70s F150 come into shop with a "no lights but runs fine issue" that was a frozen and corroded foot switch. I replaced the switch and wanted to see if I could recreate the issue by holding the switch half way between hi/low, it did.
Typically that would make the headlights inop but everything else is on different terminals of the light switch. I could see a bad light switch, but not understanding how a bad headlight dimmer switch would affect dash lights etc unless it was shorted to ground. Electrically it doesn't make sense
