12 volts power outlet repair

First thing to do is to figure out if it's a problem with the socket or the power going to the socket. You'll need a voltmeter or a 12V test light to check the center tap on the outlet and verify it has power. If not, disconnect the power wire going to that tap and see if that has power. If it does, then you most likely need to replace the outlet, and if not go check the fuse feeding that outlet.

Once you've done that, come on back and let us know what you found.