1968 mustang interior courtesy light issues

Hello. There isn't really any secret to it. You'll have to take your volt meter, start at the fuse box, check both ends of the fuse to see if power is actually passing through it, move around the circuit in steps, checking to see if power is making it to that point, and go until you find the point that power is not making it past, and fix whatever it is that's interrupting the circuit. If power is making it all the way to the bulbs, then you ever have a ground problem or the bulbs are bad. Hope that helps.

Hi again. So, they just needed a little vacation? :gringreen That would seem to indicate a problem with the headlight switch or headlight switch connector. If everything keeps working, cool. Problem solved. Just be aware of what it just did if your car decides to start doing something else weird with the lighting at some point in the future. Begin your search for a solution with the question, "Could the headlight switch or connector cause this to happen?" If yes, that's where you want to start.