Doesn't come on no matter the lights & dimmer position?
Did you try jumping it from the marker light connector to see if they came on?

Those lights are usually individualy grounded (one wire into the light), not run in paralell (two wires per light), so one shouldn't kill all. And even if your ground in one cluster got corroded & went out, the other should work. So, either the main power wire from the switch has grounded or broke, or the rheostat on the switch is bad. And yes, sometimes switches just fail, PITA, but happens.

1956 GMC 370 dump " 'Tater "
1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI

I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion! :P