Determining Function Of Trailer Taillight Wires on Horse Trailer Taillights.

Updated 04/11/2016 | Published 04/07/2016

Question:

There are 3 wires coming out of the back of my tail light on horse trailer on each side right side has the yellow,green,and black. Left side has the same. My plug in on trailer wiring is white ground, yellow, left side,brown,and green. What wires connect?

asked by: Jennifer S

Expert Reply:

Since yellow, green, and black are not standard trailer taillight wires, we will need to do a little more digging to find the functions of the different wire colors.

To determine the function of the trailer taillight wires, you will want to trace the wires into the taillight housing. The wire that makes contact with the outside of the bulb socket is the ground wire. Once you've determined which wire is the ground wire, you will want to ground this wire and apply 12V power to the other two wires, one at a time.

One of the wires will activate the trailer taillights. This wire will be connected to the brown wire on your trailer's 4-Way connector. The other wire will activate the trailer's brake and turn signal. The brake light should be noticeably brighter than the taillight. This wire will connect to either the green or yellow wire from the 4-Way, depending on which side of the trailer the light is located.

For the wires coming out of your 4-Way trailer connector, you will want to run the yellow wire to the left-hand stop and turn light wire, the green wire to the right-hand stop and turn light wire, the brown wire will need to connect on both the left- and right-hand sides of the trailer for the taillight function, and the white wire will need to be grounded to the main trailer ground at the front of the trailer.

expert reply by: Victoria B