Trailer Brake Lights Work But Turn Signals Do Not Work

Updated 09/29/2024 | Published 05/22/2013

Question:

I went to buy a utility trailer at Tractor Supply and when they hooked to the wiring I had only brake lights and no turn signals. I checked the t connecter with a meter I put the black lead on the white wire and I checked all the leads on the plug for voltage and all of them had voltage. I checked it the plug when I first wired it and it show me the turn signals were operating. What should I think?

asked by: Harry B

Expert Reply:

Trailers use a combined wiring system meaning the brake lights and turn signals are on the same circuits. Since the brake lights are working on the trailer, and because you have tested the vehicle wiring and it is working properly, there is most likely a bad ground on the trailer.

To be certain you can try a different trailer if there is one available. You can also retest the vehicle wiring using a circuit tester to confirm that the turn signals do work on the vehicle side trailer connector.

If the vehicle side trailer connector has dirt or corrosion build up then that can cause the problem as well. Cleaning out the pins may be all you need to do. The constant draw of the brake lights is stronger than the intermittent draw of the turn signals so it may overpower any additional resistance such as dirt or corrosion. But the turn signals, having less draw, could be affected by it.

If it is a ground issue start by making sure the vehicle side and trailer side connectors are grounded to clean and corrosion free bare metal surfaces. Do the same for the lights on the trailer. If the trailer has a tilt bed, folding tongue, or aluminum frame, you will need to run jumper wires from the light grounds to the main trailer connector ground.

I have included some links that should help you.

expert reply by: Michael H

Mary T.

9/28/2024

I'm new at diagnosing and repairing trailer issues and my right trailer blinker does not work. Where do I look to see if the side connector is grounded?

Robin H.

9/29/2024

@MaryT you need to check the ground on both the vehicle and trailer side connector. There is no exact spot so you need to trace the white wire on both connectors back to where it contacts the metal to check the ground. While you're tracing it I would also make sure the wire isn't damaged. Make sure it is secure on a clean, bare-metal surface. If you check this and it still isn't working I would check for power on the vehicle side. If you don't have power at the vehicle connector work your way back until you find the problem. If this is an aftermarket vehicle wiring harness and you have power going into the converter box but not coming out you will need a replacement wiring harness. If this is a factory wiring harness check the fuses to make sure they aren't blown.