Four wires need to match when wiring a trailer hitch. The running light wire colors are yellow, green, brown and white. Larger trails use more wires for separate running lights on the side of the trailers.
The green wire is for the right turn signal. The yellow wire is for the left turn signal. The brown wire is for the trailer’s tail lights. All these wires should be a minimum of 18 gauge. The white wire is the ground wire, and should be at least 16 gauge.
If the trailer has more wires, a blue wire is used for the electric break control. A red or black wire is used for the fuse block. Finally, a purple wire is used for the backup lights.