not really sure, but honestly, if your going to have to run a wire down from the positive terminal of the battery, it should be easy to do a clean installation.
you could go from the terminal, right to the open part of fender. feed it down, take off rocker or even just open it up enough to feed wire thru, then from there i guess zip tie it to like the brake lines or something similar.
or go down the fender, into the interior, pop off interior trim, like the sill plate area. then tuck up into the plastic pieces in the rear seat area, rear seats fold down, so tuck it there, go under carpet, find an opening to get from inside trunk to outside underneath. and voila. haha.
how heavy duty of a hitch are you planning on putting on your stang?
personally, i'm not big on splicing wires. wiring has never been my strong point. i'm getting better with it, but i don't trust myself enough to mess with factory wiring. i installed a boost gauge in my friends car, and the sodering on that was easy, but i didn't mess with anything factory.
+ not messing with the factory wiring, makes everything a reversible process.