7-Pin Round to 4-Pin Flat Blade Trailer Plug Adapter, Waterproof Trailer Light Plug Connector, 7 Way to 4 Way Trailer Converter for RV Truck Caravan Utility Tow Vehicles. 【7 Pin to 4 Pin】: This trailer plug adapter is a standard 7-pin round and 4-pin flat converter that connects tightly to the socket, allowing you to tow your camper or boat trailer without using the vehicle’s electric brakes, thus increg your work efficiency.