How to convert a 4 way flat trailer plug to a 7 way round trailer plug. Trailer Wire repair. - YouTube
Amazon.com: 4-Way Flat Trailer Connector with Snap Self-Closing Lid Cover Heavy-Duty 12V 4-pin Trailer Tow Wire Harness Socket Kit with 7.8" Wires Road Tough WeatherLock : Automotive
Wire a Trailer
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
4-Flat to Dual 4-Flat Splitter | U-Haul
Hopkins 4-Wire Flat Connector, Vehicle to Trailer Wiring Connector in the Trailer Parts & Accessories department at Lowes.com