Troubleshooting Trailer Brakes Locking Up When Connecting 7-Way To Tow Vehicle

Question:

Should there be current to the trailer brakes, eve when the truck brakes are not pressed? Bought a old 1978 single axle tow behind. Was changing a trie for our first trip. When I plugged in the harness the brakes locked up. Im confused now. Everything else work as should. Could the brake terminal be actually connected to the 12v auxiliary instead of brakes?

asked by: Gary K

Helpful Expert Reply:

It does sound like there is either something not wired correctly or you have a short in the wiring which is causing the trailer brakes to activate and lock up. There is also the possibility of having an issue with the trailer breakaway switch If the pin is missing, broken or damaged internally connecting your vehicle could provide power to the breakaway switch which activates the brakes.

I recommend starting by checking the condition of the wiring along the 7-way and also check inside any Junction Box # 3375601101 if there is one present on your trailer. This will also allow you to remove the 12 volt charge line coming from your vehicle which will help you to determine if the issue is from the breakaway switch or in the wiring after the 7-way connector. Depending on your comfort level with wiring you may need to contact a mobile technician or nearby shop to have it looked at. I have linked an article below which goes into 7-way wiring a little deeper which will help you to check and troubleshoot the wiring if you are comfortable with electrical wiring.

expert reply by: Bud M