Replacing OEM Trailer Wiring Harness with # 118336 for 2004 Honda Pilot  

Question:

Expert Reply:

Lets begin with the purpose of the converter box. The wiring system that trailers use is very simple. The turn signal and the brake lights are carried on the same circuit. The left turn and brake light signals are carried in the yellow wire down the drivers side of the trailer, and the right turn and brake light signals are carried on the green wire running down the passenger side. This is the tried-and-true system that has been used for years.

The converter comes in when you have a vehicle that uses a separate bulb (usually amber in color) that carries the turn signals. Because the brake light and turn signal are now carried on different circuits, the converter is used to combine the signals onto the same circuit, just like the wiring system the trailer uses. If you look at the photo of the converter box that I edited for you, you can see that there are more wires going into the input side than the output side.

We have a video that helps explain the combined-versus-separate wiring, click on the link.

The number one cause of converter failure is a wiring short on the trailer. At some point in your trailer wiring, the copper wire conductor has come into contact with the trailer frame, and creating a short circuit which in turn, damaged your converter box. Before proceeding with replacing the converter box, you will want to locate and repair the short in the trailer wiring. Trace each circuit back from the trailer connector, and follow each circuit back to the light fixture. Look for broken or pinched wires, or cracked or worn wire insulation.

I cannot speak to the factory practice of having the trailer connector attached to a bracket outside of the vehicle. I know from experience that having the connector inside the vehicle, protected from the elements is preferable. If you would prefer to run the trailer connector to the outside location, you can look on the underside of the vehicle for a grommet that could be used to pass through the connector under the vehicle. If one is present, it would usually be located in the cargo area floor, under the carpet. If the existing hole is too small to allow the connector to pass through it, the connector would have to be cut off and re spliced. You would want to cut and splice as close as possible to the converter, so that the splices remain in the vehicle, protected from the elements. Make sure that the area around the wire where it passes through the sheet metal is sealed with silicone, to prevent exhaust gas from entering the vehicle.

I have linked install instructions and an install video that you might find helpful.

expert reply by: Mike L

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