Do you mean the "cigarette" 12V socket. I replace the one in my 88 GT years ago and picked one up at Auto Zone/Advanced Auto in the HELP section in the electronic area. The original one was burned out. It was one of the easier simple repairs I ever did.
It is possible to disassemble the original and replace the bad socket. You must bend back a locking tab and unscrew the sleeve that goes around the socket. Then you can slide the socket out of the mounting flange. Assemble in reverse order. I don't have a part number for the socket, I just bought a generic replacement that was the same length as the original. It must be the same length, as there are threads on the end of the socket that the sleeve screws onto.