Troubleshooting Malfunctioning Tail/Running Lights on a Basic 4-Way Trailer Wiring System

Updated 11/11/2009 | Published 11/10/2009

Question:

All lights work except tail light on basic 4 way connection have tried new bulbs any suggestions

asked by: Joe

Expert Reply:

First thing to check would be the connector at the vehicle. The brown wire is the the taillight/running light circuit. Use a circuit tester, like part # PTW2993, to make sure that the post with the brown wire on the vehicle connector is getting power when you turn on the head lights. If everything works properly at the connector, then move on to the trailer wiring.

The wires on a 4-Way system are as follows: white = ground, brown = taillight, yellow = left side blinker and brake, green = right side blinker and brake. Make sure these wires on the trailer are not frayed or loosely connected. Check the instructions that came with the light kit, if any, and make sure the lights are wired according to the instructions. Ground connections are often a cause of problems. Check to make sure the ground connections of the lights are directly contacting the metal on the frame as paint can sometimes insulate an electrical connection. If you can write back with the light kit part number, I should be able to provide more specific instructions for troubleshooting.

expert reply by: Patrick B