I am not an electrician but maybe something to do with electrical system sensing the load or resistance or lack thereof? I do know LEDS use less current and some systems need resistors installed for the lighting to work correctly.
The idea of returning to stock is just a step in diagnosing problem since that may be the only thing you have changed and if problems show up after the change then maybe the change is the problem....
After that you would probably need a voltage meter to check for current draw and grounds on each circuit to eliminate a bad circuit or ground on trailer and the AV, just my guess on that one though.