Troubleshooting Wiring When Left Turn Signal And Brake Do Not Work On Trailer

Updated 03/01/2016 | Published 02/28/2016

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16 Gauge, 4 Conductor Bonded Parallel Wire - Per Foot

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Question:

what color does the brown and yellow wire connect to on the plug coming from the truck? We can get brake and right turn signal on the right e side of trailer but cannot get brake or left turn signal on the left side of trailer although I have running lights on both sides.

asked by: Earl

Expert Reply:

When checking wire harness functions on your truck connector I recommend using a circuit tester like part # PTW2993. Have someone sit in the cab and go through the functions and test each pin on the connector.

On a typical wiring installation with a 4-way connector, the white wire will be your ground. The green wire will be connected to your right turn and brake. The yellow wire is connected to the left turn and brake, and the brown wire will be connected to your running lights.

It sounds like the brown wire is run correctly but the yellow wire is not. Check to see which pin on the connector shows current when the left turn is used on the truck and make sure the yellow wire on # 16-4B-1 is connected to that mating pin on the trailer connector.
I have attached a link to a helpful article about trailer wiring you can check out.

expert reply by: Jeffrey L