Troubleshooting Trailer Wiring Where Brakes Lock Up When Connected to Truck

Published 10/08/2019

Question:

I’m using a 7 blade plug tho. It was a 6 plug and i changed it to 7, cause thats what my truck is. I was using an adapter, but when I started having issues I replaced the 6 with a 7. Is there someone im wiring wrong on the 7 that’s causing this?

asked by: Kevin C

Expert Reply:

This is a very common issue on trailers that use 6-way connectors as there is two different ways that 6-ways get wired typically and the only difference is that the brake controller output circuit and the 12 volt accessory circuits are swapped. So what that means is that all you have to do is swap the two circuits on the trailer wiring and you'll have fixed the problem.

The picture I attached shows a 6-way pin out that you'll need to use to swap the circuits properly.

expert reply by: Jameson C

click to enlarge

Kevin C.

10/8/2019

Jameson C.

10/8/2019

This issue still sounds like it's related to the 6-way wiring issues I mentioned. Best option is to verify that you have all of the circuits correctly wired to the 7-way on the trailer as it still sounds like the two circuits happen to be swapped. Most likely you'll just need to swap the pin in the 11:00 and 7:00 position as you look at the front of the connector. See second diagram. If nothing else you might still verify all of the wiring pins of your 7-way by running a jumper wire from a positive battery post to all of the pins to see what activates.