I was using a 7-way to 4-pin wiring adaptor identical to this harness:
This adaptor didn't come with instructions so I assumed it was simply plug one end to the 7-way and the other to the TV's 4-pin. Turns out the ground wire with the ring terminal needs to be attached to either the trailer or the TV frame. Lights worked fine (w/ headlights off) which led me to falsely assume the adaptor was correctly hooked up.
