Troubleshooting Trailer Brakes that Intermittently Lock Up While Making Left Turns

Updated 11/27/2015 | Published 11/26/2015

Question:

When returning home from a trip I started having trailer brake problems. At first when I was pulling into a service station to fill up I felt my truck kind of dipping in the rear and it felt as is I might have a flat. When I checked I could find nothing wrong. We continued on our way and then later when I had to brake to slow the trailer brakes braked as soon as I just verily touched the brake pedal. I checked my brake controller and lowered the gain but there was no difference. I then lowered the gain to zero and still no difference in the braking. It felt as though I was pressing hard on the brakes. Then I had to make a left turn and as I did so the brakes on the trailer braked let up braked again let up again braked again causing my tow veh. to dip to the side as I was making a 90 degree turn. During this braking I was not pressing on my brake petal. In fact I was trying to accelerate pressing on the gas petal. I was finally able to pull over to check what was wrong but could find nothing. I even checked the breakaway controller and it was fine. Have any idea what is happening?

asked by: Wayne M

Helpful Expert Reply:

Your left turn/stop light circuit is shorting out to the brake output circuit of your trailer wiring. Normally when this happens it is the right turn signal circuit since the pins on a 7-way of these two circuits are right next to each other.

What you need to do is check the wiring and connectors on both your tow vehicle and trailer looking for anything that would allow these two circuits to short together. Typically it's cut or exposed wire but it can also be corrosion.

expert reply by: Jameson C