CURT 58034 Vehicle-Side and Trailer-Side Square 6-Way Trailer Wiring H – Camp-Out Inc.
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
Hopkins 4-Wire Flat Connector, Vehicle to Trailer Wiring Connector in the Trailer Parts & Accessories department at Lowes.com