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 7 Wire Trailer Harness | eBay 7-Way Trailer Adapter Custom Plug Wire Harness Converter Adapter. 4 wire flat to 7-way RV blade round. Allows the user to create custom plug in wiring systems for any towing situation. Commonly used w..