Est. 2008
Current Version ISO 25981:2020
Scope 7-pin 24V connectors for liftgates
Regionality Worldwide

The truck-and-trailer connector system according to ISO 25981 was established in 2008. Its purpose is to define a standard for the connection and supply of technical equipment in trailers which has a high current consumption - e.g. tailgate lifts or electrical forklifts. It can be used for applications with a nominal supply voltage of both 12V and 24V as the system detects the voltage and limits the current to 50A.

The sockets and plugs according to ISO 25981 are physically similar to the components of the ABS/EBS connector system according to ISO 7638-1/-2. However, plugs and sockets of both standards are not mateable. For a better visual differentiation, the ISO 25981 components are of gray color.

Electronic monitoring of trailer equipment

Used in combination with an additional electronic monitoring device, the connectors according to ISO 25981 effectively protect the complete charging system against damage by overvoltage, misuse and electrical arcing. Within this setup, the socket provides two control pins (pin 5 and 6) to signalize the electronic monitoring device whether a trailer cable is connected or not. For a correct charging function, one of these wires is connected to minus (e.g. in the battery box of the trailer). This coded connection does not only result in a turn-on signal for charging the additional battery pack but, in addition, the feedback system of the platform at the trailer is determined. With a hybrid operation (i.e. the towing vehicle and trailer have tailgate lifts from different tailgate manufacturers with different feedback systems), the correct coding of pin 5 or 6 results in a correct switching principle of the feedback signal in the driver's cabin. In this way, it is possible to combine trailers with different minus feedbacks from all tailgate manufacturers with a towing vehicle that is equipped with a comparable electronic monitoring device (with trucks, the feedback signal is always minus operating current principle).

Scope of the standard ISO 25981

The standard ISO 25981 specifies dimensional characteristics, contact allocation, tests and requirements of 7-pole connectors for electrical connections of electronically monitored charging systems of towing and towed vehicles.

This electrical connection is intended for use with separable truck-trailer combinations in order to connect an additional battery pack of the trailer with the generator of the truck using an electronically monitored charging system.

ISO 25091 further specifies a park socket used to receive and store the plug when it is disconnected.

Contact Allocation for Connectors According to ISO 25981

 Contact no.FunctionCross-sectional areaCore insulation color
1Plus charging current; switched on electronically6 mm²red
2Plus charging current; switched on electronically6 mm²white/red
3Minus charging current6 mm²brown
4Minus charging current6 mm²white/brown
5Switched on minus, if platform is closed (control pin for switching on charging current and feedback signal for systems following quiescent current principle)1 mm²blue
6Switched on minus, if platform is opened (control pin for switching on charging current and feedback signal for systems following operating current principle)1 mm²brown
7Switched on minus for feedback signal, if tailgate lift of trailer is opened1 mm²yellow