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Troubleshooting Trailer Brake Lights Not Working With 2021 Ram ProMaster 2500


Hello, I purchased and installed the trailer kit ITEM # 118618, pretty easy install. ram promaster van 2500, 2021 I then added the 4 to 7 adapter. ITEM # 30717 I hooked up the trailer and nothing. My friend hooks it up to his truck and it works. So I tested the 4 pin, and get good ground, right, and left, but no brake lights. Turn signals also work. On the 7 pin, i get a good ground, rgith and left lights and turn signals, but again no brake lights. Also I loose the right and left lights with the brakes are applies. I also connecting the black 12v power from the 7 pin, and no imporvement to a fused line. Please help, why wont it work?


Expert Reply:

To begin troubleshooting this problem I recommend checking the connections on your T-One Vehicle Wiring Harness # 118618. Often when one function is not working it is due to a set of connectors not seated together properly. Try disconnecting and reconnecting the harness to ensure the connectors are seated together properly.

While you are checking the connection it might be a good idea to give the wires a quick inspection. Although it is a new wiring harness, it is possible a wire got pinched or nicked resulting in a short.

Another thing you can try is moving the ground to a different location since a bad ground can cause strange issues like this. Realistically the brake lights should work since the turn signals work and they run off of the same wire as the brake lights.

I have attached a helpful article on troubleshooting 4-way wiring for your reference. I lists troubleshooting steps in detail for a variety of different problems. If this does not get your brake lights working please reach out and I will help you troubleshoot further.

expert reply by:
Robin H

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