Brake Light Stays on When Trailer is Disconnected

Updated 04/21/2020 | Published 11/11/2018

Question:

We have a new dump trailer and the left brake light stays on all the time even when it isnt hooked up. When we plug it into our truck the truck throws a code check emergency brake on trailer. What does this mean and what is wrong with the trailer? Do we need to completely rewire our trailer or do we need to replace our breakaway box?

asked by: Chelsy

Expert Reply:

If you can tell me the year, make, and model of your tow vehicle I can then look up what the code is referring to but if not you can find this info in your owner's manual. If the left brake light stays on all the time even with the trailer disconnected then you have a short between this circuit and most likely either the auxiliary or breakaway battery on your trailer. You will need to trace this wire back from the tail light assembly all the way to the trailer connector while checking or breaks. We find that on dump trailers it is typically a short where the bed tilts.

Please let me know what you find.

expert reply by: Conner L

Ryan

4/20/2020

I have a similar problem on my Maxxd Dump trailer. I have a 2018 F150 that reads left light fault. My left break light stays on even when it is unplugged from the truck, im assuming from power from the battery for the hydro lift. The funny thing is when I take the 12v 20a circuit relay out the light will turn off. With it still being out i can hook up my pig tail to the truck and my lights will operate correctly.

Chris R.

4/21/2020

It definitely sounds like that circuit is somehow drawing power from the dump trailer battery. The only thing I can recommend is to try and trace the wiring up from the right tail light to check for any exposed areas that are making contact with a nearby wire or the trailer frame, repairing as needed.