7-PIN type S connector (24V)
- Updated:
- By: Kevin van Mierlo
Contents
Definition
The 7-Pin S-plug is used in 24V systems as an additional connector to the N-plug. Where the N-plug provides the basic lighting, the S-plug provides additional functions such as:
- Constant power supply
- Battery supply for trailer functions
- Reversing lights
- Power supply for cooling motors or relays
This configuration is defined in ISO 3731 and was the standard in heavy transport and agricultural equipment for a long time, before the introduction of the 15-PIN connector (ISO 12098).
Wiring diagram of the 7-PIN S (24V) connector
| PIN | Function | Colour |
|---|---|---|
| 1 | Battery charging current | Grey |
| 2 | Reversing lights | Black |
| 3 | Mass for PIN 1 | White |
| 4 | Free / auxiliary function | Green |
| 5 | Free / auxiliary function | Brown |
| 6 | Mass for PIN 2 (constant current) | White |
| 7 | Constant power supply | Red |
ISO 3731 standardisation for 7-PIN S connector 24V
The (24V) 7-PIN S connector is specified in ISO 3731 and was mainly used in older vehicles and trailers with additional electrical equipment. Read more about ISO 3731
Applications of the 7-PIN connector
Although the 7-Pin S connector is increasingly being replaced by the 15-PIN standard, it still remains relevant in specific niches of Heavy Transport, Agriculture and Industry. The S connector is essential in places where a separate, additional power supply is required in addition to basic lighting:
- Special transport: trucks and tractors equipped with separate power circuits for functions not directly covered by the basic lighting.
- Additional power supply: agricultural machines or implements that require continuous current (PIN 10) or relay-controlled power supply for monitoring, small hydraulic pumps or charging of onboard batteries, for example.
- Older systems: The connector is necessary to ensure compatibility with older trailers, semi-trailers or containers that are still in use and where conversion to a 15-PIN connector is not cost-effective.
View TRALERT® lighting for heavy-duty agricultural vehicles and agricultural trailers:
The switch to 15-PIN connector (ISO 12098)
The functions of the N and S plug are combined in modern vehicles in the 15-PIN connector. It is more reliable, waterproof and prevents errors.
Adapter use is possible, but not recommended in professional applications.
CAN-bus interference and LED lighting
Do you use LED lighting on a trailer with an S-connector and a modern vehicle with a CAN-bus system? If so, problems may arise, such as:
- Lighting not working
- Fault codes on the dashboard
- Overheated cabling in case of faulty load
CAN-bus solutions for LED lighting
Blog: resolving CAN-bus interference with LED lighting
Frequently asked question
Why have N and S plugs been replaced by the 15-PIN connector?
The dual-plug configuration (N + S) was error-prone and cumbersome. With the introduction of ISO 12098, a single, combined, reliable connection has been adopted that is suitable for all functions in heavy-duty vehicles and trailers.
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Author
Kevin van Mierlo
Lighting expert at TRALERT® - Kevin tests lighting and finds out everything about legislation. He can tell you all about it.
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