Stop/Turn Signals Work on Trailer but Tail/Running Light Circuit Does Not

Question:

Hi experts, EZ loader boat trailer with 4 pin harness. Brake and signal lights work, but running and marker lights failed last night. Less than one year old. Tow vehicle is 2016 GMC Sierra. Where to start? Thanks in advance.

asked by: Neil

Expert Reply:

Start off by checking your connectors to ensure that they are both clean and free of corrosion. Once you have verified this then the next step is to check your fuses. If those look good take a tester like part # PTW2993 and verify that the pin next to the ground pole (see attached photo) is receiving the tail/running signal.

If it is receiving the signal, then that means the problem is on your trailer. If you don't get a signal, then the problem is on your 2016 GMC Sierra. Either way, you need to start by checking your grounds to ensure that they are all securely connected to a clean, bare-metal surface. After that simply move on to the wiring for the tail/running light circuit and make sure everything is not damaged or pinched.

You will likely find one of the things mentioned above as the problem. Let me know if this doesn't work and I can help you troubleshoot further.

expert reply by: Jon G