How do I Diagnose My Left Turn Signal Not Working on My Trailer?  

Question:

Expert Reply:

The first thing I always like to check is the tail light bulb. It sounds simple, but it could be a simple fix. Sometimes the connection is poor and unplugging and re-plugging the bulb will fix that connection.

If the bulb is good, I like to check the left turn pole on the 4-way or 7-way on your tow vehicle. I have attached articles to help you determine the correct wires on your plugs. When you're checking the circuit, I suggest picking up a circuit tester like part # PTW2992. Testing the connector will tell us if the problem is on your vehicle or the trailer.

If the problem is on your vehicle you need to check your fuse panel for a blown fuse. If the fuses are all good and the bulb is good, you should check for a bad ground. If there is a bad ground wire you need to disconnect the battery and run a new ground wire.

If you're still not getting the signal there could be a spot in the wiring that is grounded out or spliced on your trailer. Follow the left brake wire back to the plug and check for cuts or exposed wiring.

If everything is okay at the vehicle's connector, you need to fully check the trailer wiring, from the plug and follow the wires all the way to the tail light. If there aren't any bad wires it most likely is a bad ground. You need to check the ground wires and replace the fouled wire.

expert reply by: Clayton O

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