Troubleshooting Trailer Wiring That Locks Up Trailer Brakes When Vehicle is in Reverse

Question:

I have a 2017 Ram 3500 and a 16Ft trailer. 7 pin connection, All working fine. Then I had the trailer converted to a fifth wheel tongue. I had to use extension wires to make the distance. All brake lights, turn signals working fine but when I reverse, the trailer brakes engage. Truck says no trailer connectedinch but I havent found a ground problem or connection problem. Help!

asked by: Karen P

Expert Reply:

It sounds like the wiring adapter/extension you're using has a different configuration for its pins/functions than the standard 7-way format. There are actually three formats for 7-ways, and you can see all of them in the linked article on trailer wiring. It simply sounds like your extensions either have a short or corrosion, or they are wired differently, with the reverse light signals getting into the circuit for the trailer brakes.

You can apply a circuit tester like # PTW2993, shown in the linked video, to the socket pins to confirm which function is on each one and use a battery to test the trailer functions.

expert reply by: Adam R