I had my 2004 Liberty wired to tow behind our RV about a year ago. This weekend I bolted on the MOPAR hitch and plugged in the module for the trailer hitch wiring. On the trailer - the brake lights, turn signals and four-ways all work, but running lights (when headlights are on) do not work.
My guess at the moment is when they wired my Liberty to be towed behind the RV they snipped or disconnected wiring somewhere (perhaps behind the tail light lenses). I am hoping there is an easier answer out there.