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Troubleshooting Boat Trailer With No Working Lights After Installing New Lights and 7-Way Connector


I recently re-wired my boat trailer with new lights, all new wiring and a new seven way plug. I just bought the boat about two weeks ago and the lights didn’t work when I bought it so I figured I would replace them because they kind of looked old anyways. I tested each individual pin on my truck and they all read out to over 12.5 V. For some reason when I plug the trailer in, the lights don’t work at all, well sometimes they barely blink but I mean you got to get up real close to see it. And my parking lights oh my truck blink with my brake lights. If I unplug the trailer my lights are fine on the truck. Please help me if you can


Expert Reply:

I would be happy to offer some troubleshooting steps to get your boat trailer lights working.

Since all of the lights are having an issue I recommend using a circuit tester like the # PTW2993 to test power wires to each of the lights on the trailer with your 7-way connector plugged into your truck and each of the functions on. If you have power to all of the lights but no lights you have a grounding issue. Depending on the lights you purchased they may ground through the mounting hardware, or have a ground wire. Either way you will want to make sure they are grounded securely to clean corrosion free metal.

If your boat trailer is aluminum your best bet is to route all of the ground wires to the main grounding point on the tongue of the trailer to make sure you are getting a good ground. A bad ground can cause all kinds of weird issues.

If you reused the original trailer wiring running to each light it is possible that it was damaged prior to you owning it and there is not a full 12 volts running to each light which could cause the issues you are seeing. If you didn't run new wires to each of the lights I recommend replacing all of the wiring running from the 7-way connector to each of the lights with 12 gauge # 12-1-1 for the ground, 12v power circuit, and trailer brakes (If electric), and # 16-1-1 for the running lights, turn signals, brake lights, and reverse lights (If installed on your trailer).

I included a link to a helpful article that goes over

expert reply by:
Samuel C

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