Check for ground
My first trip on my towed the lights did not work either. I was meticulous in making sure everything was perfect. Still, no working towed lights. I checked this, that and everything else. Still no worky. Finally, I checked for a proper ground. I had attached my ground wire on the towed to a piece of it's undercarriage frame, not bodywork. I never checked it for being a PROPER ground previously. Why should I? It's the frame. It's gotta be a ground!! Well, it turns out that with a test light from the battery and probing the so-called ground wire terminal in the plug-in...no ground. Must be a broken wire, I thought. Followed the wire path, not broken. Used the positively connected test light again and probed the connection point to the frame NO GROUND!!! I probed all over that chunk of framework and no ground. Probed a different area and found a good ground, attached my wire going to the plug and the lights have worked ever since.
1. not everything under a vehicle these days is grounded to the battery...check it.
2. The towed and the tow vehicles are 2 distinctly separate electrical systems, therefore their ground must be connected. In my case it is via the umbilical and the 2 connectors
Randy & Karin B, Mattawan, MI
2016 Newmar Bay Star Sport 2705, 18,000# F53
Blue Ox Alpha & Baseplate, Equinox & RViBrake2, Blue Ox rear Trac Bar, CHF+, RSSA