Instrument lights workaround?

Make sure the tail/ parking light terminal has power. The light switch has TWO power feeds, and the headlights 'only' power does NOT power the dimmer. Most of those dimmers, you can inspect and test visually and externally. Most of them are open and accessable. You should be able to probe and see if you have power feeding the dimmer, as well as inspect the wiper for dirt/ damage/ corrosion.