Taillights come and go (no not the turnsignal)

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My son's 68 has a taillight/brake light that comes and goes.The wires are fine, no breaks or bare spots, but i think he has issues with the socket. We have cleaned it and the bulb up and works for a while and off again. If you wiggle it it comes and goes as well. I have not found a place to just buy a socket and wires to splice in. Is there a socket"tightening" trick or anything else to try before replacing the whole fixture? Thanks