Usually you can just locate the relay that supplies power to the circuit from the ACC contact on the ignition switch, pull it
and jumper the socket to bypass the relay.  I tdid this on the power windows in my '85 4Runner:
    http://www.4crawler.com/4x4/CheapTricks/index.shtml#PowerWindows

Here is a writeup on the same mod on a 3rd gen 4Runner:
    http://www.top4runners.com/ja/electrical.html#poweroutlet

Or, as suggested in another reply, just re-wire the socket with a dedicated wire from the battery.  This is what I did on mine,
since I had blown the fusible link on it.  My dedicated power feed is much more stable than the factory circuit that seeme to
have a lot of voltage variation.

--
  Roger