Troubleshooting Trailer with Non-Functioning Turn Signal Lights Behind a 1992 Toyota Pickup

Published 03/02/2010

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Question:

The brake lights and turn signals and running lights are contained in one bulb on the trailer, however on the Toyota truck the brake lights and running lights are one bulb and the turn signals are another bulb on a separate curcuit. The wiring harness is installed correctly, the ground is good, The brake lights and running lights work fine, I have no turn signals on the trailer. I have turn signals on the truck. Please advise

asked by: Fred M

Expert Reply:

This is the right harness for your 1992 Toyota Pickup. It sounds like you might be having a ground issue. Check the ground wire from the harness. Make sure it has direct metal to metal contact with the frame or body. Rust, corrosion and paint can insulate an electrical connection. Check the grounds for the tail lights on the trailer, make sure they have good metal to metal contact. Finally, check the the trailer ground wires, make sure again, that they have good metal-to-metal contact.

You may also want to double check that you have the half of the harness with the brown and yellow wires on the driver side of the truck and the red and green side are run to the passenger side.

expert reply by: Patrick B

Fred M.

3/2/2010

Patrick B.

3/2/2010

The black converter box on harness # 118379 combines the separated brake and turn signals from the truck and combines them for the sake of the trailer We can isolate the problem to narrow the search a bit. Disconnect the trailer from the truck. Using a circuit tester, like part # PTW2993, test the 4-Way connector. Clip the tester to the truck frame as your ground, and test the brown, yellow and green wires to make sure they function properly. Brown is taillights, yellow is left turn and brake, and green is right turn and brake. If the connector does not work as it should either there is a problem in the installation, or the converter is bad. If all the functions at the connector work the problem is on the trailer. Check bulbs and wiring connections. Check to see if wires are frayed or nicked. Most trailer electrical problems are results of bad grounds, so keep an eye on these.