First thing you should do at this point is test the 4-way of the wiring harness with a circuit tester part # PTW2993 for voltage on all of the right pins when the taillight signals are being applied. Just like in the video I attached.
If the voltage checks out there but the trailer lights still don't function right then the problem is on the trailer wiring. That would mean that problem is either due to a ground issue or a short issue.
Make sure that the trailer side connector are clean... view full answer...
It sounds like there's too much going on with the controller for it to be a faulty unit. I suspect that the controller might be wired to the wrong stoplight switch wire, and my Curt representative agrees. Use a circuit tester like part # PTW2993 on the wire you have the red brake controller wire attached to. In the 2008 model, a purple/white striped wire was used, but I have no information about a 2007. This wire should show power ONLY when the brake pedal is pressed, not with the turn... view full answer...
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