My driver's side rear courtesy light on the sail panel isn't working. All the other interior lights are working. I assumed it was a bad bulb, but when i changed it, still no light. The contacts for the bulb inside the housing are clean. I'm assuming that the issue isn't related to a fuse or a door jamb switch, because if those go bad then none of the interior lights would be working. So do any electrical experts out there have any ideas as to what might be going on?
Bad socket or wiring. You'll have to find where you are losing continuity, simple as that. See if you can remove the sail panel bezel and see where the wiring goes. Then trace it back to see where the problem is.
In my 70GS, the wire harness for the sail panel courtesy lights goes down and connects into the Intermediate harness in the back of the trunk. Just behind the back seat on driver side. The wires were orange and white (I believe). One pair runs up above the wheel house up into the sail area and the second pair runs along the top edge of the trunk under the package tray area over to the passenger side. Like Larry said, check for continuity. If passenger side works, the door switch has to be working, so there has to be a cut on the driver side. The orange and white wires have ends on them that are only crimped on and they slide into the plastic housing for the courtesy light. So the socket is actually the crimped on ends and the actual housing. Heck, the second bulb could be bad as well. See if 12V is present without shorting the ends to the body.
I had a similar problem on my '69--I thought the bulb had died but when I banged on the cover, it would start working. Bad connection somewhere close to the housing.