Wiring Trailer Lights with a 4-Way Plug (It's Easier Than Each light will have 3 wires: one that connects to the main harness's brown running light wire, one that connects to the turn/brake light wire (typically yellow or green), and a white ground that should be secured to the trailer frame. Use a crimper to strip back the insulation on the wires. Then, use a butt connector and heat gun to connect the wires. Connect any additional ground wires from your lights. Related searches for trailers lights wiring diagram 4 wire trailer wiring diagram7 pin trailer harness diagram6 wire trailer wiring diagram7 wire trailer wiring diagram4 flat trailer wiring diagram7 round trailer plug wiring diagram7 pin trailer wiring diagram with brakes7 prong trailer plug wiring