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Running Lights Are Not Working On a Trailer Towed by a 2008 Honda Odyssey

Question:

can you give me some ideas on what to check if my day lights wont work on my trailer but brake and signal lights are? thanks.

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Expert Reply:

The typical cause of trailer running lights not working is a bad ground connection but there are some tests you can do to determine where the problem is. First, disconnect the trailer from the tow vehicle. Then use a circuit tester such as # 40376 if you need one to test the connector on the vehicle. Have someone sit in the vehicle and turn on the running lights while you test the connector with the circuit tester.

If the running light circuit works at the trailer connector then the issue is on the trailer. If they do not work then the issue is on the vehicle.

Common causes if the malfunction is on the vehicle is a blown running light fuse (use owners manual to find fuses), a bad ground, or a blown converter box. Make sure the main ground for the wiring harness is attached to a clean and corrosion free bare metal surface. If it is connected to a bunch of other grounds try moving it to a different location.

If the problem persists the next step is to test the converter. First test the wires going into the box from the vehicle. If there is no running light signal going into the box then there is a problem with the vehicle wiring that you will need to have checked out.

If the signal is correct going into the converter, test running light wiring on the output side. If there is no signal coming out of the converter but there is one going in then the converter is bad and the harness will need to be replaced.

If everything checks out on the vehicle then the issue must be on the trailer. Make sure the trailer connector is clean and free of corrosion. Then make sure that the main trailer connector ground and the grounds for all of the lights are attached to clean and corrosion free bare metal surfaces. You can also inspect the wiring for any breaks that need to be repaired.

If you have an aluminum frame, tilt bed, or folding tongue, or have recently installed a plastic license plate frame between a light ground and trailer frame, these thing could cause a ground problem. Running jumper wires from the light grounds to the main trailer connector ground can help. I have included a link to an article that covers how to test and troubleshoot wiring and a video showing how to test a converter for you.

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