When you say you have power at the socket, do you mean you checked the wire going into the socket, or did you actually test the bump on the inside of the socket that the bump on the bulb presses against? If you only tested the wire going into the socket, then you need to test to make sure the power actually made it through the back of the socket in the bump that touches the bump on the bulb. If you tested the bump inside the socket and have power there, then you are down to one of two things. You either have a bad ground, or the bulb is not good. You said you have a good bulb, did you just look at the filaments, or did you actually test it with a lead wire and grounding it against your battery to make sure the bulb comes on? I have traced many electrical gremlins, and sometimes it’s something you overlook or assume is OK. With power going to the inside of the socket, and a tested, known good bulb in the socket, if it does not work, try touching a wire to the side of the socket that should be the ground to a known good ground. If the bulb comes on, then, you know that somewhere inside the socket, you have a grounding issue. I believe you said the other bulbs in that housing worked. Is this housing one that has the socket pop into the back of it? If so, the grounding issue could be inside the socket like you mentioned, OR it could be where the socket pops into the housing. But if the other bulbs in that housing are working, and you know, the bulb is good, and you have power going to the socket, it boils down to either a grounding issue between the housing and the socket, or a grounding issue inside the socket between the wall of the socket and the bulb. I can’t think of anything else it could be.
