Troubleshooting the Left Side of the LED Combination Tail Light Kit Not Functioning Properly

Question:

I purchased a new wiring harness kit for my boat trailer from etrailer. I started installation yesterday and everything went well until I tested the wiring. The rear right tail light works well however I cant get the rear left tail to come on with the brakes or blinker. I have done some cleaning of the plug on my truck and the left tail light still doesnt work. As I looked over the plug on my truck in the attached photo it only has 4 wires. I then looked at the new plug on my trailer in the attached photo and I noted there are 5 wires which includes 2 brown wires. Are these 2 plugs compatible? If so, I will have to do some more cleaning and maybe some other troubleshooting. Thanks in advance.

asked by: Tom C

Expert Reply:

It looks like you got the LED Combination Tail Light Kit # TLL9RK, not just a new wiring harness. The plug on that kit is compatible with your 4-way.

I would start by checking the ground connections for the trailer side connector and the lights. Poor ground connections are the most common culprit of trailer wiring issues. The lights will have either a ground wire or they will ground through the mounting hardware. Each of the ground connections should be secured to a clean, bare metal surface on the trailer frame or to the negative terminal of a trailer battery if you have one.

If the ground connections check out fine, then I would start at the trailer side connector. With the trailer connected to the tow vehicle, use a circuit tester # PTW2993 to test the left side stop/turn and running light circuits. Probe the wires, past the trailer connector, at different points working your way toward the trailer lights. This will tell you if there is a signal on those circuits and, if so, where the signal terminates.

If you do not have any signal on the left stop/turn or running light circuit, then the issue could be in the connector itself. The pins could be bent or damaged. If you wired the connector yourself, remember to wire the connector to the socket by function, not color. Aftermarket manufacturer wiring and even OEM wiring can use different colors for corresponding functions.

expert reply by: Scott S