Left Side Trailer Lights Not Working But All Other Lights are Fine

Question:

Have replaced all wiring on trailer and ne connector on trailer that plugs into truck which is 7 way and trailer is 4 way. How are the colors to match up to both connectors. On connector have Red, white, green, yello, blue black and brown.

asked by: Linda

Expert Reply:

On a 7-Way trailer connector usually the wire functions are green for running lights, black for 12-volt power, yellow for reverse lights, brown for right turn/brake lights, red for left turn/brake lights, blue for electric trailer brakes, and white is ground.

With that said it is best to test the connector using a circuit tester such as # PTW2993 while someone sits in the truck and runs through the lighting functions.

On the trailer, the 4-Way will have the one covered pin as the ground. Next to it is the running light pin, then the left turn/brake light pin, and the last pin is right turn/brake lights.

If power is getting to the trailer's connector and back to the lights but they will not light up then the issue is a ground problem most likely. Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light but can show up any time.

Make sure that the vehicle side and trailer side connectors are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces.

The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

expert reply by: Michael H