Troubleshooting 4-Way Trailer Connector without Drivers Side Brake/Turn Function at Connector

Question:

I have a 4 way connector on my boat trailer. Suddenly the left turn light on the trailer stopped working. All marker lights work fine and the right tail light and tun signal work fine. The left tail light comes on when the lights are turned on but the turn signal, brake light and 4 way flasher on the left side is non existent. I created a cross over cable and swapped the outputs at the truck to the trailer. Now the left side works when the right turn signal is on and right side does not work eliminating trailer wiring. I checked the output voltages at the connector on the truck and the yellow wire has no voltage. I disconnected the connector from the wiring harness on the truck and the yellow wire has no voltage. The yellow wire is the left turn and stop signal. Im not sure what to do next? Any suggestions

asked by: Allen H

Helpful Expert Reply:

You have done a great job isolating the problem. The trailer wasn't the issue, so I recommend returning that to its original state as a jump wire from the right to left side will only allow the right side functions. I've attached an article to assist.

Since you have determined no voltage at the truck connector, I recommend you disconnect the US Car Connector and check for the signal there as it may be a simple connection issue. If it is not an issue there, you will need to trace that wire using a circuit tester like # PTW2993 to find the short and replace that section of wire with # 16-1-1. If you cannot find the short, I recommend having a mechanic take a look at it as the harness may need to be replace as this is a factory system.

expert reply by: Jason S