Installing a Trailer Wiring Harness on a Trailer with Yellow, Black and White Tail Light Wires

Updated 09/03/2014 | Published 08/31/2014

Question:

I have the same harness as is described with this part number but my tailights have a yellow, black and white wire coming out of them. How are these suppose to be connected to the harness?

asked by: Nate

Expert Reply:

When it comes to tail light wiring, black is usually the running light circuit and white is usually ground. That would leave the yellow wire for the brake light and turn signal. On trailers, the turn signal and brake lights are combined on the same circuit.

When installing a harness like the Optronics Wishbone 4-way Harness, # A35W42B, the green wire would connect to the yellow wire on the passenger side tail light and the brown wire with the green stripe would connect to the black wire from the passenger side tail light. It will also be used for all of the marker lights on the right side of the trailer.

The yellow wire will connect to the yellow wire from the driver's side tail light and the brown wire with the yellow stripe will connect to the black wire and all marker lights on the left side of the trailer. The white wire from this harness and the white wires from the tail light assemblies should be grounded to a clean bare metal surface on the trailer frame.

I have attached our help article on trailer wiring that should help when rewiring your trailer.

expert reply by: John H