Image result for 4 pin trailer wiring diagram | Trailer wiring diagram, Trailer light wiring, Utility trailer
How to Install Trailer Wiring | U-Haul
TowSmart 7-Way Blade to 4-Way Flat Trailer Light Wiring Adapter 1415 - The Home Depot
4 to 4-Way Round-to-Flat Trailer Plug Adapter | West Marine
Amazon.com: Oyviny 4-Way Flat to 7-Way Round Blade and 4 Way Trailer Wiring Harness Adapter Vehicle-Side 4 Pin to Trailer-Side 7 Pin and 4 Pin Dual-Output Connector with Mounting Bracket for Truck