7-Way Trailer Connectors

What it is

SAE J560 defines the 7-conductor round-pin connector used on heavy trucks, tractors and commercial trailers. The socket (receptacle) is mounted on the tractor, usually at the back of the cab. The trailer has a nose box or front receptacle. A coiled cord (the "pigtail" or "light cord") with a plug at each end connects the two. The center pin is used for the auxiliary circuit, which on most trailers powers the trailer ABS. Pin functions and wire colors are on the 7-way trailer wiring chart.

How to identify

A J560 plug has seven round pins in a circle of six with one in the center, a keyway so it only fits one way, and a spring-loaded lid on the socket that latches the plug. Housings are zinc die-cast or high-strength plastic. Cords are marked with conductor sizes and often with a count such as "7 cond." The RV and light-truck 7-way uses flat blades instead of round pins. It is a different connector (SAE J2863) and does not mate with J560.

Parts and what to match

Key points

• Corrosion at the pins is the most common cause of lighting and ABS faults. Use dielectric grease as the maker allows and keep lids closed.
• The center pin must carry power continuously for ABS on trailers that need it. Check that the tractor wiring provides it.
• Many cords use heavier conductors for the ground and the auxiliary circuit. Match conductor sizes when ordering replacements.
• Sealed plugs and sockets with molded backs keep water out of the wires. Rebuildable plugs need careful sealing.
• Check pin tension. A loose plug causes flicker and intermittent ABS warning lamps.

Common mistakes

• Ordering an RV blade 7-way for a commercial trailer, or the reverse.
• Splicing a damaged coiled cord instead of replacing it.
• Leaving the socket lid open so water and road salt get in.
• Mixing up circuit assignments when rebuilding a plug. Follow the wiring chart pin by pin.

Governing standards: SAE J560 (seven-conductor electrical connector for truck-trailer jumper cable). FMVSS 108 for lamp functions served by the circuits.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.