Hopkins Manufacturing Corporation makes your towing experience simpler and more rewarding through innovation and value. Hopkins offers a variety of towing solutions including vehicle wiring kits, adapters, vehicle and trailer connectors, breakaway systems and much more. Today, more than 40 percentage of retail category sales are generated from Hopkins innovations. A 4 wire flat is the most commonly used trailer plug. This plug is found on small boat, utility, jet ski, snowmobile, and small camper trailers where right turn/brake, left turn/brake, tail/marker lights and ground is needed.