Saskatchewan!
Great province....my wife's family is there!...now back to your situation.
There is a 75% chance this electrical problem is tied to a bad ground somewhere....everywhere, particularly on a 52 year old truck.
You have to work this through all of the possible grounding points for your lights.
You can always make an external ground wire with a good aligator clip or probe to do this.
Barring that....you might have a 1157 (dual element) bulb that has had its second filament break and spring over and touch the other element...which causes a world of weird lighting/circuit problems. Ask me how I know...lol.
However this is easy to check by simply substituting a new 1157 bulb everywhere whilst checking the electrical/lighting result.
However....start with the very very probable grounding problem.
All Good
Coley
