7 Pin Trailer Wiring Harness | etrailer Install a 7-way, RV-style trailer connector on your vehicle with this easy-to-splice harnessLite draws power directly from the battery to avoid overloading your vehicle's circuits. Brake electrical system Includes harness with 4-pin connection point for plugging in a brake controller wiring adapter (sold separately) Supplies required fuses, wire taps, and additional hardware Constructed Amazon: 7 pin trailer wiring harness Amazon: 7 pin trailer wiring harness. OPT7 Weatherproof 7 Way Flat Blade to 4 Way Pin Adapter w/Secure Tab - for Trailer Tow Hitch and Redline Tailgate LED. 4.5 out of 5 stars 321. $7 $ 7. 99. NEW SUN 4-Way Flat to 7-Way RV Blade Trailer End Electrical Adapter Plug.