This van has the dual batteries, and according to the power distribution box under the hood, the second battery is mostly for a tow trailer's electrics. I can't seem to find a wiring harness on the frame rail in back, or anywhere for that matter. Do I need to tap into the tail lights? Won't that defeat the purpose of the second battery?

 

If the second battery was for a camper, it would really only power the one 12 volt aux wire.

A regular tow harness has a seperate relay for running lights, and seperate fuses for left and right trailer turn. You may also have a fuse for electric brakes. All this would not be hooked to the second battery.

If you do have a towing package, the factory would have put a trailer plug in the rear, or if they had wires back there, they would have them taped well, up in the harness.