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
CURT Electrical Adapter (4-Way Flat Vehicle to 7-Way RV Blade Trailer) 57184 - The Home Depot
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
7-Way Round to 4-Way Flat Pin Adapter For Trailer Tow Hitch & Redline Tailgate LED – OPT7 Lighting Inc