jellyroll

I intend to add 1 or 2, 55 watt aux backup lights attached to the trailer hitch. The normal backup lights are way too weak for me to see safely behind me. I plan to tap power for the lights from the 12v outlet in the luggage compartment. I need a 12v signal for the solid state relay used to switch the new lights. It looks like it will be difficult to run a wire to one of the backup lights in the rear hatch. Is there an easy way to get access to the 12v reverse signal without running a wire to the passenger compartment or hatch? I have NAV, but assume there is no 12v reverse signal coming from the unit below the luggage floor. If I can only get access in the passenger compartment, where is the best place?