Horse Trailer Brakes Activate Without Vehicle Brake Pedal

Updated 01/17/2020 | Published 01/15/2020

Question:

the brakes on my horse trailer are locking up when I try to pull forward, even though I am not stepping on the brake pedal. The digital readout shows .c.

asked by: Harry H

Expert Reply:

The '.C' means that there is a trailer connected and isn't an indicator of a problem.

Are you by chance using an adapter in the 7-way connector to change it to a 6-way? If you are, there are two common ways to wire that connector. One uses the center pin as the brake output, the other use the center pin as the constant 12-volt power supply to the trailer. If the vehicle is wired one way and the horse trailer the other, it would certainly explain why the brakes immediately apply when the trailer is plugged in. Most adapters like # 47549 can easily be disassembled and have the black and the blue wires swapped.

95% of the time we hear about an issue such as this, this ends up being the problem.

expert reply by: Mike L

Harry

1/15/2020

both the plugs are 7 pin, the center pin doesnt have any power going to it. Should I switch the blue and black wires in the controller to see if that works?

Jason S.

1/17/2020

Trailer 7 way connectors won't have the pins reversed but there are two ways they are wired. Heavy duty trailers like commercial or agriculture trailers will often have auxiliary 12V power where the traditional setup will have reverse lights on that center pin that will only show power when the vehicle is shifted into reverse. I recommend using the attached article and going through each wire function using an incandescent bulb circuit tester like # 40376. That will help you determine if the wiring to your 7 way is correct or not based on function and location.

Helpful Links

faq-wiring-7-way.aspx

tv-review-Draw~Tite-circuit-tester-40376.aspx