The original wiring harness came from the light switch all the way to the socket on the drum taillight. Most repro harnesses make you splice the wires as Mitch mentioned. Sacremento Vintage Ford makes the correct harness for the drum taillights.
The wires push into the socket, and you should be able to pull them out. I'd spray some Kroil into the socket and use a thin ice pick or some such tool to try to pry a little to the side, just to loosen the spring loaded contacts a bit.
To remove the socket from the light body, you need to push the small brass peg in, then carefully twist and pull. Again, I'd spray some kroil on the metal body, as it's usually rusty around the socket.
I type too slow, Ron beat me to it.