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
Reese Adapter 7 Way Round to 4 Way Flat in the Trailer Parts & Accessories department at Lowes.com
Hopkins Plug - In Simple 6 - Pole Round to 4 - Wire Flat Adapter - 47315 | Blain's Farm & Fleet