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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
Your Guide to 4-Pin Trailer Connectors | Car and Driver