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SAE J2691-2020: Engineering the 15 Pole Connector for 12V Towing Systems
The SAE J2691-2020 standard establishes minimum construction and performance requirements for a 15 pole connector between towing vehicles and trailers, designed for 12 VDC nominal applications. It supersedes J2691 APR2018 and is aligned with SAE J2742 for connecting cable requirements. This connector accommodates both power and ISO 11992-1 signal circuits, along with dual ground wires to handle grounding requirements within the terminal capacity constraints.
Scope and Structural Specifications
The SAE J2691-2020 standard defines the minimum construction and performance requirements for a 15 pole connector used between towing vehicles and trailers with 12 VDC nominal supply. It applies to trucks, trailers, and dollies, and is designed to work with SAE J2742 connecting cable. The connector accommodates power circuits and ISO 11992-1 digital signals, with dual ground wires for robust grounding.
Key Structural Features:
- Floating contacts: Contacts align to datum position when plug and socket engage, ensuring reliable connection.
- Automatic closing covers: Socket and park socket covers close automatically upon disconnection, preventing debris ingress.
- Mis-mating prevention: Design ensures no contact can be made without excessive force, preventing incorrect connections.
- Contact designation marking: Numbers permanently marked on cover and terminal faces (minimum 2 mm height).
The connector position and free space must comply with ISO 4009. The locking lever design must consider space for socket fastening screws as shown in the standard’s figures.
Contact Allocation, Wiring, and Grounding
The contact allocation is specified in the table below, along with wire colors and functions. Special attention is given to the dual ground circuits (terminals 1 and 8), which must be bonded together to provide adequate current capacity.
| Contact No. | Function | Wire Color |
|---|---|---|
| 1 | Primary Ground (common with terminal 8) | White |
| 2 | Clearance Side Marker and ID Lamps | Black |
| 3 | Left Turn Signal/Hazard | Yellow |
| 4 | Stop Lamps | Red |
| 5 | Right Turn Signal/Hazard | Green |
| 6 | Tail and License Lamp | Brown |
| 7 | Ignition Power for ABS and Running Gear PLC4 Trucks | Blue |
| 8 | Secondary Ground (common with terminal 1) | White/Green/Stripe |
| 9 | Cab Switched Auxiliary Power | Orange |
| 10 | Reserve | Pink |
| 11 | Constant or IGN Auxiliary Power | Purple |
| 12 | CAN_H (Unshielded) ISO 11992-1 | White/Yellow |
| 13 | CAN_L (Unshielded) ISO 11992-1 | White/Green |
| 14 | Reserve | White/Black |
| 15 | Reserve | White/Orange |
Note: For ECBS equipped tractors or trailers, only LED lamps shall be utilized on relevant circuits.
⚠️ Important: Dual Ground Circuit Bonding
The tractor and trailer ground cabling interfacing to the SAE J2691 receptacle (terminals 1 and 8) must be bonded together, forming a common ground termination. The bonding point should occur at the termination points of the SAE J2691 receptacle interface wiring within the tractor and trailer. The combined circular mil area (CMA) of these two ground circuits is greater than a single ground circuit, but neither alone equals the single ground found in SAE J560. Therefore, it is imperative to create a common parallel ground circuit within the cabling architecture.
Terminal Sizes: The standard specifies wire sizes and terminal sizes for different contact groups: Contacts 12-15 use 0.8 mm² wire (AWG 18) with 1.5 mm² terminal; Contacts 2,3,5,6,9,10,11 use 3.0 mm² wire (AWG 12) with 4.0 mm² terminal; Contacts 1,4,7,8 use 5.0 mm² wire (AWG 10) with 6.0 mm² terminal. The connecting cable must comply with SAE J2742.
Testing and Frequently Asked Questions
Connectors must pass rigorous testing according to ISO 4091, with specific requirements including connection and disconnection forces not exceeding 100 N. Environmental tests include salt spray per ASTM B117 and UV exposure per ASTM G153/G154. The standard also includes specific requirements for mis-mating prevention.
🔍 Design Insight: LED Lamps for ECBS Systems
For tractors or trailers equipped with Electronically Controlled Braking Systems (ECBS), only LED lamps shall be used for lighting functions. This prevents interference with the CAN bus communication (ISO 11992-1) and ensures proper operation of the braking system.
Frequently Asked Questions
How do I ensure proper grounding with dual ground wires?
Terminals 1 and 8 must be bonded together at both the tractor and trailer interfaces to create a common parallel ground circuit. This is essential to achieve the required current-carrying capacity. The bonding design is at the discretion of the OEM, but must result in a common ground termination at the receptacle wiring.
What wire gauge should be used for each contact?
Refer to Section 5.4 of the standard: Contacts 12-15: 0.8 mm² (AWG 18) with 1.5 mm² terminal; Contacts 2,3,5,6,9,10,11: 3.0 mm² (AWG 12) with 4.0 mm² terminal; Contacts 1,4,7,8: 5.0 mm² (AWG 10) with 6.0 mm² terminal. Always size terminals appropriately for the conductor.
How is mis-mating prevented between plug and socket?
The standard requires that it be impossible to make contact between any tube or pin of the plugs and sockets without excessive force. The dimensional tolerances and floating contact design ensure proper alignment and prevent mismating.
What tests must the connector pass?
Connectors must be tested to ISO 4091, which includes mechanical, electrical, and environmental tests. Specific requirements include connection/disconnection forces ≤ 100 N, resistance to salt spray per ASTM B117, and UV exposure per ASTM G153 or G154.
By following the SAE J2691-2020 standard, engineers can ensure a reliable, standardized electrical interface for towing vehicle-trailer combinations, supporting both conventional lighting and advanced digital communication systems like ISO 11992-1 CAN bus.
