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
Conntek 10305 7 Way to 4/5 Way Flat Trailer Plug Adapter
CURT Electrical Adapter (4-Way Flat Vehicle to 7-Way RV Blade Trailer) 57184 - The Home Depot