Trailer Brakes Locking When Lights Turned On

Published 12/28/2016

Question:

I havent pulled my trailer in about a year and when I went to use it yesterday it seemed to fine but when it got dark and I turned on my headlights the trailer brakes locked up. I turned the lights off and the brakes released. At 1st I thought it might have something to do with my truck since I had never pulled with it before 2015 Toyota Tundra 4x4 with Brake Controller installed but when I hooked it up to the truck 2003 Ford F250 I normally use it is doing the same thing. As long as I dont turn on the running or headlights then it pulls fine but the moment I turn on the lights the front right brake locks up. Have you seen or heard of this before?

asked by: Gail A

Expert Reply:

This isn't the first time I've heard of this type of issue. It sounds like the functions of your trailer wiring are not synced with your truck. Because you have used two trucks, the issue appears to be with the trailer. I've attached a picture to help, because I think your brakes on your trailer are being connected to the running light function on your truck. There also could be a short between these two circuits because they are side by side. If that is the case, replace the connectors # HM47210 and # H20046.

I suggest running thought each function to check it against the attached photo. Change the functions to match if they are out of place and don't trust color as it is often connected wrong...match function.

expert reply by: Jason S