When you get the headlight switch fixed, turn the **** all the way to the left till it clicks, and the domelight should come on. That will test part of the circuit.
If it doesn't come on, I would pull the sill plate off the driver's side rocker panel, and you will find a channel where the wiring runs for the domelights and a few other things. Follow these wires along as the go to the rear cab corner area. These wires like to get corroded and damaged, and one of them does feed the domelight.