Troubleshooting Trailer Brakes that Lock Up When 7-Way Connector is Connected

Published 10/25/2023

Question:

my breaks are locking up when 7 pin, which tests in working condition, is connected. I can disconnect the break control wire and no change. Breaks will only unlock if 7 pin connecter is removed. Can only move trailer forward or backward about a foot. Merritt stock trailer in excellent condition including wiring. Something other than break controller seems to be feeding voltage to break system.

asked by: Mike

Expert Reply:

Sounds like the 12 volt accessory circuit is shorting out to the brake output circuit on the trailer wiring. Go over the wiring and look for any cut or exposed wire between these two circuits and fix as needed.

If the stock trailer had a 6-way connector on it that was adapted to a 7-way the problem is that there is two different ways that 6-ways can be wired and only difference is the brake output and 12 volt circuits are swapped so if that's case that would be what you would need to change.

expert reply by: Jameson C