Troubleshooting Boat Trailer With Non-Functional Lights on One Side  

Question:

Expert Reply:

The best way to troubleshooting trailer wiring is to disconnect the truck and trailer and test each one separately. This makes it easier to isolate the problem.

The start is to make sure all trailer ground wires are solidly connected to clean bare metal surfaces. Often a bad ground can cause your issue.

Your F-150's trailer connector can be tested with a circuit tester like # PTW2993 while you have a helper activate the functions on the truck. The linked video shows how to use the tester on the connector's pins while your helper turns on running lights, turn signals, etc. The linked article includes photos of different trailer connectors so you can find yours and see which pins to test. If you find a problem in the truck's wiring harness, you can use the link provided to select a replacement.

If the truck connector is okay, then you can move on to the trailer and test it directly using a 12V battery. Apply the battery negative to the trailer ground pin and apply the +12V wire to each circuit on the trailer, one at a time, to see if the lights operate with this direct power feed.

If the lights on the trailer work when tested this way, then you may have dirty or corroded connectors. Use a spray-on contact cleaner (available from auto and electronics stores) on the truck and trailer connector contacts to remove any signs of corrosion. An article on troubleshooting wiring is included for you as well.

expert reply by: Adam R

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