An auto's trailer hitch is located adjacent to the tow package. It transfers electrical signals from the vehicle's circuits to the trailer's by means of a detachable plug and cable attached to the trailer's tongue. The hitch itself is attached to the auto's circuits by means of a harness usually molded into the hitch itself, so electrical connections only have to be made where the harness joins the supply wires.
Consult the auto's owner's manual to learn how to gain access to the wiring circuits that operate the auto's rear light clusters. This is usually achieved by removing a trim panel on either side of the cargo storage bay. The floor covering in some autos is molded to cover the sideways; in others, the wiring is slung from supports in the upper rim of the sidewalls.
Split the green wire of the four-conductor harness molded to the hitch away from the other three wires. Route the green wire to the back of the passenger side rear light cluster, and the remaining three wires to the back of the driver's side rear light cluster.
Join the wires of the trailer hitch harness to the appropriate wires in the auto's harness using either cable splices or by hard-wiring them. Cable splices simply clip over the two mated wires, immediately making an electrical connection and insulating the join at the same time. Hardwiring requires removing a 1/2-inch of insulation from both wires, using wire strippers at the end of the hitch harness wire and a craft knife at a convenient location along the auto's wire, then twisting the wires together, making the join with a soldering iron and insulating it with a shrink-wrap kit.
The color-codes used for the hitch harness wires should be as follows: white to ground, brown to the tail lights circuit, green to the right turn blinker and yellow to the left turn blinker. Auto manufacturers do not subscribe to a universal color code for their wiring, so consult the schematics in the owner's manual to learn the appropriate pairings.
