ISO 3731:2003 specifies the dimensional characteristics of, and specific requirements for, 7-pole connectors of type 24 S and their contact allocation for the electrical connection of towing and towed vehicles with 24 V nominal supply voltage, thus ensuring interchangeability. A 24 S connector is intended to be used in addition to a 24 N connector according to ISO 1185 where more than 7 poles are required.