66 c10 electrical issue

[88Stanger]

Gotta love electrical... LOL

So when I do Electrical personally I start at one end or the other and typically I take the easy end, the actual plug for the light. Using a test light, test that you have power there.... if you do it could be a bad light bulb, connection to the ground area or bad ground connection outside the bulb case. If no power there, start working your way back until you get a good power signal. Sometimes the issue is quick and simple other times it is in the worst of places. As another has mentioned, having a wiring diagram for your truck is worth its weight in gold. I as others do have a copy of the assembly manual for our trucks and inside it are the wiring diagrams, just an FYI. Good luck though