Morning BB
If there's no accessory socket anywhere (unusual these days, maybe in the glove locker?) its possible to wire in your own. Motor factors will have all you need.
If its easy, connect to the positive battery terminal with a soldered eye terminal and take it immediately to a fuse of its own. After that fuse you can continue inside the cab to a location of your choice. If you use 28/0.30 cable, it will conduct to 17.5 amps, much more than you need. That's 28 strands of wire, each being 0.30" diameter.
The return can connect to any metal part of the body, again with a soldered eye terminal.
If however this socket could be used for a fag lighter at any time, I'd upgrade to a thicker cable. I don't know what your accessory will draw current wise so start with a low fuse rating, say 5 amp.
To get from engine bay to cab, find a convenient grommet, use a sharp point to pierce it, and feed the cable through there. Don't use crimp terminals, and don't squash the cable in to any metalwork.
If there is an accessory take off anywhere, so much the better but I can't help on that one!
John
