7-Way Trailer & RV Plug Diagram - AJ's Truck & Trailer Center It’s the dreaded 7-Way Trailer & RV plug that we all have come to know and love. Most new vehicles equipped with a tow package have connectors. Trailers with electric brakes need them too. The 7-Way Trailer Plug is around 2″ diameter connector that allows an additional pin for an auxiliary 12-volt power or backup lights.[PDF] Trailer Wiring Diagrams | etrailer - ActionOutboards 7-Way Round Trailer Connector (Flat Pin) 7-Way Round Vehicle Connector (Flat Pin) 7-Way Round Trailer Connector (Round Pin) 7-Way Round Vehicle Connector (Round Pin) 7-Way Connectors Aside from the three main lighting functions, additional pins for electric brakes, a 12 volt "hot" lead, and backup lights are available. There are two types of 7 ISO standards for trailer connectors - Wikipedia Trailer connectors between the trailer and passenger car, light truck or heavy trucks with 12V systems. In Europe, both 7-pin (ISO 1724) and 13-pin (ISO 11446) are common. The 13-pin version being phased in is newer, provides more services than the 7-pin, a more positive locking and also better protection against moisture and contamination. Parts of a Trailer Hitch - Essential Towing Equipment - Towing 101 A trailer wiring harness is a length of wire at the back of a vehicle that allows its electrical system to connect to a trailer. Integrated with the vehicle's existing wiring, it provides a standard connector, such as a 4-way flat plug.