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
Seven-Way RV Blade to Four-Wire Flat Adapter with Flex Cord
Trailer Wiring Adapter - 4 Way Flat to 7 Way Round | Meijer
Reese Connector 7 Way Round Car End in the Trailer Parts & Accessories department at Lowes.com
Conntek 10436-048 7 Way to 4 Flat Trailer Adapter With Spring Cable