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How To Wire New 4-Way Wiring Harness To Trailer That Has White, Black, Red, and Green Wires


On my trailer, I have white, black, red and Green wires. My harness has white, yellow, brown and green wires. Trying to get the right wires from the harness to the trailer. Does the brown need to be split since it’s the running lights?


Expert Reply:

I would be happy to help, but you will need to confirm what functions the wires on your trailer perform as they are not the standard colors.

There are a few ways to do this. The easiest is if you have not removed your current trailer connector, plug it into your tow vehicle and turn on each turn signal, and turn on the head lights while testing each of the wires with a circuit tester such as the # PTW2993. Write down the functions so you do not forget or get them mixed up.

If you already removed the trailer connector you will want to find which wire is the ground. This will be connected to the frame of the trailer. Once that is found connected each of the other three wires to the positive terminal of a 12v battery to see which light function lights up. Again write down the function of each wire so you do not forget or get them mixed up.

Once you have identified the functions you will need to make the following connections to your new standard harness:

Running light wire to the brown wire on the new harness.

Right side turn signal to the green wire on the new harness.

Left side turn signal to the yellow wire on the new harness.

Trailer ground tor the white wire on the new harness.

You are correct that you will either need to splice the brown wire on the new harness as it needs to run to all of the lights on the trailer, or your can use a wishbone harness such as the # A35W42B and has two brown wires, one for each side of the trailer, to make wiring up the lights that much easier.

No matter which harness you go with you will want to use heat shrink butt connectors # DW05744-10 for a weather tight connection.

I included a video review of the # A35W42B being installed along with a link to a helpful article on trailer wiring for you to take a look at.

expert reply by:
Samuel C

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