I installed an aftermarket backup camera for which I took 12V + and - off the trailer hitch (7 pin). I can actuate the camera from my aftermarket head unit (JVC KW-AV60BT) manually and it works fine. However, there is a trigger lead on the head unit that I can connect to a reverse lamp lead so that the camera view is automatically triggered when I put the truck in reverse.

I realize I could run a wire from the head unit all the way to the rear bumper and tap into one of the wires on the reverse lamps to use as a trigger for the head unit. I'm hoping someone can point me to an easier (and closer...like in the cabin or under the hood) location to tap into the same wire. Anyone know what I need to do? Thanks.