Hey Master Tech, I just reread the whole thing, and I didn't see any evidence of trying a direct ground to the socket either, but pretty solid evidence that there wasn't a ground on that wire from any of the sources. He hadn't yet reported his findings from the triage of that yellow wire. We all are trying to reach the same destination, but with different methods or goals. Unregistered User has already determined that there is power at the lamp socket, but no ground. We can safely assume that the bulb will work when the circuit is completed. He's now at the point of finding the break in the wire supplying ground. The circuit can't be bypassed by just grounding the socket. It could, but would defeat the purpose of the switches. The bypass, If necessary, will have to go to the last good connection.
Sorry if I offended you. I'm 73 years old, am a retired IT Technician, and have been in electronics since 1961.

 

I had a problem with no power to dome lights, radio, and power windows. First, check if fuse #17 (I.O.D.) is good. If it is good, replace your door jamb switches. I replaced mine and it works like a charm now.