Any ideas why my headlights don't work? 1976 Dart Sport.

These old cars are old!! I do not believe in just throwing new parts at trying to fix a problem...BUT..... Many parts are cheap on Rock Auto, so every time I get a new project, I:
Soak the dimmer switch with rust penetrant and order a new one regardless, just to have.
I always get a new headlight switch, ballast resistor or two (or three), coil, horn relay, ign. solenoid, but in my stash of parts is also new distributors, carbs, and everything just to have on hand, as I want a reliable car to drive and not walk back home. I carry some of such in the trunk just in case!!