The 7-pin plug-in system 12 V according to ISO 1724 / ISO 3732 is the most common system for electrical connections between towing vehicle and trailer with 12 V electrical system. The system is primarily used for applications with average requirements. It consists of a standard connector, type N, according to ISO 1724 and an additional plug-in connector, type S, according to ISO 3732. The additional system differs from the normal system with white housings, contact inserts and interchange-proof contact arrangement.