Overview
ISO 3732:2003 defines the mechanical and electrical requirements for the 7‑pole 12 S connector used for the electrical connection between towing (cars, light commercial vehicles) and towed vehicles operating at 12 V nominal supply voltage. The standard ensures interchangeability of plugs and sockets by specifying dimensions, contact allocation, markings, cable/terminal sizes and tests. The 12 S connector is a supplementary connector intended to be used together with the 12 N connector (ISO 1724) when more than seven poles are required.
Key topics and technical requirements
- Connector type and configuration
- 7‑pole type 12 S: plug has five spring pins (1, 3, 4, 6, 7) and two tubes (2, 5); socket has the complementary arrangement.
- Pins must be slotted to allow minimum compression length of 8.5 mm when engaged.
- Dimensions & mounting
- Detailed plug/socket dimensions and required free space at vehicle rear (compatibility with mechanical couplings per ISO 1103).
- Socket cover must close automatically; a storage/protection provision for a disconnected plug on the towed vehicle is required.
- Contact allocation & marking
- Contact functions and recommended core insulation colours (e.g., 1 = reversing light, 4 = permanent power, 6 = ignition‑switched power).
- Contact numbers must be permanently marked inside the socket cover and on terminal faces (character size ≥ 2 mm).
- Terminals & cables
- Rear terminal cable cross-sections: Contacts 1 and 5 - 1.5 mm²; Contacts 3, 4, 6 and 7 - 2.5 mm².
- Connecting cables must meet applicable parts of ISO 4141.
- Performance and testing
- Tests are specified in ISO 4091 with ISO 3732 amendments: connection/disconnection forces (connection ≤ 200 N; disconnection 50–200 N), locking/cable retention force (250 ± 5 N), endurance (1 000 cycles), temperature/humidity cycling (−25 °C to +75 °C), salt spray and current/carrying tests.
Applications and who uses it
- Intended users:
- Vehicle OEMs, trailer and caravan manufacturers, electrical connector manufacturers, aftermarket suppliers, test laboratories, and regulatory bodies.
- Practical applications:
- Trailer electrics, caravans, horseboxes, light commercial towing equipment - where a supplementary 7‑pole connector is needed to provide additional circuits beyond the 12 N connector.
- Benefits:
- Ensures compatibility and safety of towing electrical connections, simplifies design and procurement, and supports consistent field performance under environmental and mechanical stress.
Related standards
- ISO 1724 - 7‑pole connector type 12 N (normal)
- ISO 4091 - Definitions, tests and requirements for towing/towed vehicle connectors
- ISO 1103 - Coupling ball dimensions (mounting compatibility)
- ISO 4141 - Multi‑core connecting cables
- ISO 11446 - 13‑pole connector (alternative for >7 poles)
Keywords: ISO 3732, 7‑pole connector, 12 S connector, trailer electrics, towing and towed vehicles, 12 V connectors, connector dimensions, contact allocation, connector testing.
Open preview (PDF)Road vehicles — Connectors for the electrical connection of towing and towed vehicles — 7-pole connector type 12 S (supplementary) for vehicles with 12 V nominal supply voltage