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
Curt Trailer Connector Adapter - 4-Way to 7-Way RV and 4-Way Flat CURT Trailer Wiring C57672
Trailer Wiring Diagram and Installation Help - Towing 101
CURT Custom Wiring Harness (4-Way Flat Output) #56009 | Ron's Toy Shop, Inc.
CURT 10' Custom Wiring Harness Extension (Adds 7-Way RV Blade to Truck Bed, Packaged) 57010 - The Home Depot
Dr Infrared Heater 6 ft. 7-Way Trailer Plug Cord Wiring Harness, Heavy-Duty Weatherproof, Corrosion Resistant Inline Cable, for RV, Campers DR-RV106 - The Home Depot