Running Lights on 2 Trailers Not Working Towed By a 2003 Ford Ranger  

Question:

Expert Reply:

Since the issue is happening on both trailers, it seems unlikely that the trailers are the problem. So, the first step is to isolate the problem by testing the truck side trailer connector with no trailer connected.

You will need a circuit tester, # PTW2993 if you do not have one, to test the wiring. Have someone sit in the truck and go through the lighting functions while you test the connector with the circuit tester. If the running light circuit (located next to the ground pin) is not working on the truck, then you have gotten closer to the problem.

Check for dirt and corrosion on the pins. Using a wire brush will help clean out corrosion. If this does not help, then check the owner's manual in the truck for any fuse/relay locations for the tow package wiring and check to see if any need to be replaced. Testing a relay will require putting a known good one in the potential bad one's place.

If the wiring on the truck side is good, then the issue is on the trailers. To test the trailers, you will need to start at the trailer connector and make sure it is clean and free of corrosion. Then make sure the main trailer connector grounds are attached to clean and corrosion free bare metal surfaces.

Trace the wiring back to the lights and make sure there are no breaks or loose connections. All of the grounds for the lights will also need to be attached to clean and corrosion free bare metal surfaces.

If the trailers have aluminum frames, tilt beds, or folding tongues or if you recently added a plastic license plate holder between a light and the trailer frame, that could be the issue. Running jumper grounds from the lights to the main trailer connector ground can help. I have included a link to an FAQ article that should help you troubleshoot.

expert reply by: Michael H

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