How To Wire a Trailer Taillight with 5 or 6 Wires When There Is Only 4 Wires on the Trailer

Question:

How to wire a new 5 wire tail light to a 4 wire system? 5 wires colors- Yellow Green Red Grey White

asked by: Heber W

Expert Reply:

The four wires on your trailer wiring harness likely have the following functions:

Yellow - Left Stop/Turn
Green - Right Stop/Turn
Brown - Running Lights
White - Ground

In regards to hooking a taillight up to these wires, you would simply match up the functions of the wires on the taillight to the functions of the wires on the trailer. The taillight should have come with a wiring diagram which tells you which each color wire represents. If you have different color wires than the above on the trailer you'd need to test them for function using a circuit tester. I can't speak for every light nor every trailer wiring harness so I'm not sure I'll be able to answer this question as specially as you like but I have attached below an example which should help.

The Triple LED Trailer Tail Light part # CE44VR for example has six wires with the following functions:

Red - Stop/Turn
White - Ground
Black - Running Lights
Purple - Reverse/Backup

The two red wires on the light would be tied together and attached to either the yellow or green wires on the trailer depending on which side of the trailer the light is located. The white wire on the light would be attached to the white wire from the harness if present on the frame via a ground screw. The tow black wires on the light would be tied together and then attached to the brown wire on the trailer. The purple wire is unused.