Troubleshooting Logan Horse Trailer Wiring Light Functions

Updated 05/07/2020 | Published 07/13/2019

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16 Gauge, 4 Conductor Bonded Parallel Wire - Per Foot

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Hook Probe Circuit Tester

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Question:

Only the running lights on my be horse trailer are not working. Everything else works. ? Can u help

asked by: Kristin D

Expert Reply:

First thing you should do at this point is test the pins of the trailer wiring harness with a circuit tester part # PTW2993 for voltage on all of the right pins when the taillight signals are being applied. Just like in the video I attached.

If the voltage checks out there but the trailer lights still don't function right then the problem is on the trailer wiring. That would mean that problem is either due to a ground issue or a short issue.

Make sure that the trailer side connector are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces. The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

If the problem is on the vehicle side then I would first recommend you double check how the harness is installed on your vehicle, make sure all of the connections are good and tight. You should check all towing related fuses and relays as well.

expert reply by: Jameson C

click to enlarge

Jim F.

5/5/2020

Did Kristin D figure out the problem and solve it? I have the same problem on my horse trailer. I am wondering what Kristin had to do to fix the issue.

Chris R.

5/7/2020

I'm not sure we heard back from Kristin either way. Have you tested the running lights pin on the truck's 7-Way to narrow down where the issue is? If you find you aren't actually getting power to the running lights circuit, I would check for a blown fuse under the hood. Your truck's owner's manual should list the fuse location(s) for the trailer running light circuit - try replacing them to see if the issue resolves. Let me know if not.