Very frustrating I'm sure! It looks to me to be a ground problem. Go through with jumpers and grouns each componant, if this elimintates your problem, start removing them one at a time, putting it back until the problem show back up. Once it does, Bingo! One caveat, old light sockets sometimes build up a bit of rust between the body and the socket. You may need to replace a socket if this is the case. You will need to ground EVERYTHING in the circuit you turn on, grounds can backtrace through quite a circuitous path!
Good Luck!
Bill
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