Confounded by electrical short

The most aggravating issues I have had with my 1981 pickup have been intermittant electrical problems.

Right now, the vehicle starts fine and the headlights, dash board, and dome light all work. The running lights, clearance lights, license plate light, and turn signals do not work.

I have no idea where to begin to identify the location of the short. Any suggestions?

Thanks in advance.

Eric