To install a trailer wire, plug in the trailer lighting connector for the vehicle to the trailer brake controller plug. For vehicles without factory-made plugs, tap the white wire to the trailer ground point, the yellow wire to the trailer’s left turn signal, and the green wire to the trailer’s right turn signal. Connect the brown wire to the trailer’s taillights, and verify the connections using a circuit tester.
Use a 4-way connector to control running lights, brake lights, and left and right turn indicators. Most vehicles use the standard flat connectors with three male and one female end. Use the appropriate connector both for the vehicle side and the trailer side, and connect all ground wires from the lights to the chassis.
If the trailer uses electric brakes, connect the blue wire of a 7-way connector to the breakaway switch. Connect the wire to the electric brake control on the vehicle side to provide power for the brakes. The red or black wire connects to the breakaway kit and to a fused battery lead on the vehicle side. Connect the purple wire to the hydraulic coupler and to the backup circuit on the vehicle side. For vehicles not meant for towing, first remove the tail lights of the vehicle to access the required wires.