Why Does My Trailers Turn Signals Work But The Brake Lights Dont?  

Question:

Expert Reply:

If you aren't getting brake lights but you are getting turn signals, you have a bad ground somewhere. Brake and turn signals are run through the same circuit on a trailer and this will be the only viable reason for this to be happening.

With that said, I recommend first checking the grounds up at the lights. These should be clean, have a solid connection, and not be stacked with other ground sources. Stacking grounds is a pretty common practice, but it is always better to have a ground on its own designated source. If these look good, you will need to follow the wires to find the bad source. If a bad ground is located, you will need to repair it and then test the function with something like the # PTW2993. Or you can just have someone apply the brakes and stand behind the trailer.

If the wiring on your truck is aftermarket, I also recommend checking the grounds on the vehicle side as well. Odds are it's the trailer, but it never hurts to cover all your bases.

expert reply by: Lazer S

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