Brakes Lock Up On Tandem Trailer When Connected To 2006 GMC With Tekonsha Brake Controller

Question:

When connecting electrical plug into my GMC 2006 the trailer brakes immediately lock up on all 4 wheels. This is a used trailer, to make sure its not a problem from the truck connect forward I hooked it to the horse trailer and the brakes work perfect. Also should mention when hooking up to the problem trailer, I get just a slight glow of green on the controller, Tekonsha Commander when pressing the overide pad no red lights appear. Take the trailer connector out frees the brakes. The battery for the emergency disconnect is dead, so I removed that input wire from the junction box, brakes still stayed locked. Thanks for the help

asked by: Paul D

Expert Reply:

When you plug in your electrical connector to your trailer and the brakes lock up it will usually mean that the connection for the brake wire and the power wire is reversed.

You mentioned you plugged it into a horse trailer. It is common on horse trailers to use a 6-Way trailer connector. A 6-Way connector can have the center pin wired in two different ways. It can have the center pin wired for 12-volt power or it can be wired for the brake lead. If one trailer is wired for the center pin to be power and you connect it to a trailer that is wired for brakes it will immediately lock up the brakes on that trailer.

If you have a 7-Way connector on your 2006 GMC truck and a 6-Way on your used trailer and using an adapter to connect them, then it is possible that the adapter could be wired wrong. If your adapter uses the center pin for the 12V lead, and the trailer uses the center pin for the brake lead, then that could be causing your brakes to lock when you plug in the wiring harness.

I have a Hopkins Adapter 7 Pole To 6 Pole, part # 47549, that allows the center pin to be wired as a 12V lead or a brake lead, whichever is needed to match your trailer.

If you have a 7-Way connector on your truck and a 7-Way on the used trailer I would recommend testing the pins on both connectors with a circuit tester, part # PTW2993, to make sure that the functions of the pins match up accordingly.

I am including a link to a FAQ page on trailer wiring that will show the functions of the pins on both a 6-Way and a 7-Way connector.