A bit of a head-scratcher, but I'm pretty sure it's wired wrong, and that at least part of the problem involves ground.
If the Jeep is using its normal Stop/Tail/Signal lights as its towed vehicle lights, I think it needs protection diodes. Or maybe they're built into the design if it already has a special harness.
You don't want toad feeding back into coach's electrical system, as in somebody steps on toad's brakes/turns on toad's lights, while connected to coach. Likewise you don't want coach sending voltage anywhere in the toad but the lights. Modern cars have lighting fed by some computer (BCM, PCM, etc.) and you don't want he coach backfeeding power back into those black boxes.
