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Troubleshooting 4-Pole Wiring on Re-Wired Boat Trailer


I have a 2006 Honda Ridgeline. It has factory installed wiring connectors. I pull a small travel trailer and the round connector works fine with the brake controller and lights. The 4-wire flat connector is my problem. I have a small boat trailer and have rewired new lights for it. After solving a ground problem, I still cannot get the lights to work properly. I have checked with a meter and seem to only have about 4.5 volts available at the connector for the brake and running lights.


Expert Reply:

The best first step is to isolate the problem to either the tow vehicle's wiring or the trailer's.

Disconnect the boat trailer's 4-pole. Use your vehicle battery (or a spare battery) to directly test the trailer lighting on its own by connecting the 4-pole ground pin to the battery negative terminal and one by one connecting the battery hot terminal to each of the other pins on the trailer's 4-pole. If the trailer lights behave properly when connected in this manner then you know the problem is likely to be on the vehicle side. If they do not you will be able to know which wiring circuits (and which color wires) to check based on which lighting circuits do not function. Look for worn spots or nicks in the insulation especially at points where the wiring may rub the trailer frame.

With your circuit tester like # 40376 you can test the Ridgeline's 4-pole connector. I have linked an article with tips for testing and a brief video showing how to use the tester. If your vehicle 4-pole does not carry the correct signals then I suggest you replace the harness with a plug-n-play type such as # 118400. This harness install easily at your tail lights without need for cutting or splicing of wires. It will work independently of the factory 4-pole.

It may be that the wire gauge used to re-wire your trailer is not large enough to pass the full required current for your trailer's lights. At minimum we recommend 16-gauge. I suggest you again check all your grounds on the trailer, both for the main connector harness and at each individual light. All ground connections need to be made to clean bare-metal surfaces.

You may even just need to clean your trailer connectors. Even slight greenish or whitish discoloration on the contact surfaces can indicate mild corrosion that can be enough to impede current flow.

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