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Troubleshooting Trailer Light Turn Signals That Activate When Braking


I have a trailer that has been rebuilt more than once. I removed the old electrical system that was in very poor condition and replaced it with a new electrical kit Similar to Item # TLL9RK. I have had some issues as the instructions that came with the kit were...not detailed. I now have all the lights working when they should i.e. : - brakes light with depressed brake pedal - running lights light with truck lights on - turn signals work correctly with indicator and hazards I also have additional functionality. When the brake pedal is depressed the turn signal lights also come on. Is this normal operation or have I messed something up somewhere?


Expert Reply:

In both 4-pole and 7-way trailer wiring the stop and turn signals are combined for each side of the trailer. With kits like the 4-pole LED light kit # TLL9RK the yellow wire carrier stop AND turn signals for the left/driver side of the trailer and the green wire handles these for the right/passenger side.

Sometimes if the ground connections at the trailer and vehicle frames are not 100-percent tight and made to clean bare metal surfaces you can find weird behavior from the lights. So the first thing I suggest is checking both the vehicle's wiring harness white ground wire and the trailer's main white ground wire to ensure both are making solid metal-on-metal contact.

You can remove both ground wires and sand off both grounding points to expose clean bare metal. Then you can reattach the ring terminals with a protective coating of dielectric grease like # 11755 which will help prevent corrosion at those grounding points.

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