CURT Electrical Adapter (4-Way Flat Vehicle to 6-Way Round Trailer) 57183 - The Home Depot
Amazon.com: MICTUNING Trailer Wiring Harness Extension Kit - 4 Pin 25 Feet Male and 6 Feet Female Connector, 18 AWG Color Coded 4-Way Flat Wires for Under or Over 80 Inches Wide Trailers : Automotive
The Ultimate Trailer Wiring Guide for Preparing to Tow