22 4900 wiring question.

So the secondary trailer circuit is dropping to ~10 volts with any load, but here's the crazy part: the affected lights will go to full brightness when either turn signal flashes. But not even a flicker if the turn signal is on and the markers off.

So my question, do the trailer circuits go through the body controller? I can't wrap my head around what else could cause this. I haven't had time to chase the line from the 7 way to the firewall, I just jumpered black and brown together for now, and I've got full brightness again.

I did have a license light bulb go to 0 ohms a couple weeks ago, it was on that circuit. It wasn't popping the breaker, but it did bring the ground up enough to start dimming the markers. So I'm thinking that must have weakened something in the circuit (I did check all of the fixtures, all good there.)

 

Yeah, only the turn signals affected the marker circuit, not the brake or taillights. When I can, I think I'll start at the firewall before trying to trace the wire from the back of the frame forward.

 

It happens without the trailer, too. Haven't had time to dig further, yet. But even just the 5 top front lights and the 2 side markers pulled it way down.

And of course, being a carhauler, another trailer is a bit tough. 3' light cord eliminates a lot of options. LOL