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
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7 Way Vehicle Side to Trailer Wire Connector Round Plug 4Pin Flat for Ford F-150 | eBay
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CURT 4-Way Round Connector Plug (Trailer Side) 58060 - 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 RV Blade and 4 Way Flat Wire Harness – Nilight
Your Guide to 4-Pin Trailer Connectors | Car and Driver