Troubleshooting Trailer Wiring When Connecting a New 4-Flat Trailer Connector

Question:

I made a big mistake and cut off my trailer plug off of the trailer wires, without first noting which wires connected to which colored wires on my new plug. I bought a four wire plug, green and yellow for turning lights, brown for taillights, a white for ground, and a red I dont know what to connect the red to on the trailer?, The trailer has combination colored wires of green/brown stripe and yellow/brown stripe, a solid green and a solid yellow wire, with of course a white ground wire. I understand white goes to white, but about the others??? My plug is the standard four plug. I must have miss wired, because my fuse popped for the trailer taillights in my truck. Please help me, if you can.

asked by: Robert T

Expert Reply:

It sounds like you picked up a 5 wire trailer connector rather than a 4 wire connector. A 4 wire trailer connector will only have a white wire for ground, brown for tail lights, green for right turn and stop and yellow for left turn and stop. The red wire on the connector that you purchased is most likely for reverse lights or a trailer with separate turn signals such as a motorcycle trailer. If you do not have reverse lights or separate turn and brake signals, then you can simply tie off the red wire as it will not be needed.

Since the wires on your trailer do not seem to match up to the industry standard colors of trailer wires, then you will first need to determine the function of each wire. To do this you will want to use an independent power source such as a vehicle battery. If you do use a battery, be sure you ground the negative battery terminal. You could use a circuit tester, like part # PTW2993, from the positive terminal to each individual contact.

Once you have determined the function of each wire you will want to connect them to the appropriate wires on the wiring harness as I have indicated above. My guess is that the green and yellow wires with the brown stripe are both tail light wires and should be spliced together and connected to the brown wire on the wiring harness. Be sure you verify the functions of each of those wires before you make those connections.

If you test your wires and find the wires have functions other than what I have mentioned, let me know so we can go through more troubleshooting steps.

expert reply by: John H