Troubleshooting Wishbone Connector That Either Tail Lights or Brake/Turn Signals Work Not Both

Question:

I have a 5 flat plug. green, green/brown, yellow, yellow/brown and white. For some reason I can only get either running lights to both sides or brake and blinker lights to both sides. I cant get both. I have checked my grounds and they are all good. Any thoughts or suggestions?

asked by: Brandon W

Expert Reply:

From the wire coloring it sounds like you have a wishbone connector and not a traditional 5-way trailer connector. On a wishbone harness the running light circuit is split so you will not have a jumper wire run from one side of the trailer to the other. The wire color code will be yellow is left turn signal, yellow/brown is left side running lights, green is right turn signal, green/brown is right side running lights, and white is ground.

Does the connector work on the rear of your tow vehicle? You can use a circuit tester, # PTW2993, to check. If the vehicle side connector all passes all signals you know the issue is on the trailer.

I know you said you checked the grounds, but this sounds to me like the problem. The ground locations, at the trailer connector and at each light, need to be on a clean, bare metal surface. If the trailer's lights are grounded through the mounting studs, you'll want to make sure the hardware is just as clean and free of any corrosion.

If each light is well grounded and you still can't find the issue, let me know and we'll do some further troubleshooting.

expert reply by: Charles S