Trailers · Connector reference
SAE J560 7-way pinout and wire colors
The round-pin 7-way on a North American semi-trailer is defined by SAE J560. Its pin assignments are not the same as the flat-blade 7-way on a pickup or RV, and mixing the two up is one of the most common causes of a trailer that "has power but the ABS lamp is on".
What SAE J560 covers
SAE J560 is the SAE International standard for the seven-conductor electrical connector used on the truck–trailer jumper cable: the plug on each end of the cord and the socket on the tractor and on the trailer nose box. Connector maker Erich Jaeger's summary of the standard notes that it was originally issued in 1951 and last revised in 2020. The 2016 revision was titled Primary and Auxiliary Seven Conductor Electrical Connector for Truck-Trailer Jumper Cable, which reflects the auxiliary seven-pin connector the standard now also describes.
The cable that goes between the two plugs has its own standard, SAE J1067, which sets minimum construction and performance requirements for seven-conductor cable for trucks, trailers and converter dollies. Its scope describes a 1/8, 1/10, 5/12 construction: one 8 AWG conductor, one 10 AWG conductor and five 12 AWG conductors. That matches the conductor sizes the connector expects, shown below.
SAE J560 primary connector pin assignments
The table follows the allocation published by Erich Jaeger for the current edition of SAE J560. Treat it as orientation: your tractor and trailer makers' wiring diagrams govern for a specific vehicle.
| Pin | Wire color | Circuit | Conductor size |
|---|---|---|---|
| 1 | White | Ground return to towing vehicle | 8 AWG |
| 2 | Black | Clearance, side marker and identification lamps | 12 AWG |
| 3 | Yellow | Left turn signal and hazard lamps | 12 AWG |
| 4 | Red | Stop lamps and ABS (secondary power) | 10 AWG |
| 5 | Green | Right turn signal and hazard lamps | 12 AWG |
| 6 | Brown | Tail and license plate lamps, clearance and/or side marker lamps | 12 AWG |
| 7 | Blue | Continuous ABS primary power / auxiliary devices | 10 AWG |
The two heavier circuits are the ones that carry the most current: the ground return, which every lamp and the ABS share, and the two circuits that power the trailer ABS. An undersized or corroded ground is the single connection most likely to make every other circuit on the trailer misbehave.
SAE J560 vs the RV-style 7-way
Light-duty towing uses a different connector, the flat-blade 7-way covered by SAE J2863. Many consumer wiring guides describe that connector, or blend the two, and their color tables do not match J560. The differences that cause trouble:
- Red. Light-duty guides often list red as a 12 V battery charge or auxiliary line. On a J560 heavy-duty connector, red is the stop lamp circuit and the ABS secondary power feed.
- Blue. On a light-duty trailer, blue usually drives electric brakes. On a J560 air-braked semi-trailer, blue is the constant power feed for the trailer ABS, and it also carries the trailer ABS malfunction signal (see trailer ABS power and PLC4Trucks).
- Black. Light-duty guides often use black for auxiliary power. Under J560 it is the clearance, side marker and identification lamp circuit.
- The connector itself. The J560 plug has round pins and a heavier body. The two are not interchangeable, but adapters exist, and an adapter wired to the wrong convention reproduces all of the above.
White is ground and brown feeds the tail lamps in both conventions, which is why a miswired trailer often "mostly works".
The auxiliary connector
Current editions of J560 also describe an auxiliary seven-pin connector, pins 8 to 14, with pin 8 as its ground return and the remaining pins used for functions such as cab-switched power, ABS malfunction signaling and constant auxiliary power. Auxiliary connections are less common in the field than the primary 7-way, and the pin assignments you meet may predate the current edition. For anything beyond the primary connector, work from the published standard and the vehicle maker's diagram.
Checking a 7-way before you blame the cable
- Inspect the contacts. Green or white corrosion on pins or sockets, spread or loose sockets, and a missing or broken cover spring are the usual culprits.
- Check ground first. Measure between pin 1 and the tractor battery negative under load, not just for continuity. A connection that reads fine unloaded can drop several volts with the lamps on.
- Check each circuit at the trailer end with a known-good tester, switching each function on in turn.
- Check constant power on pin 7 with the ignition on. If it is missing, the trailer ABS may be running on the stop lamp circuit alone, which only powers it while the brakes are applied.
- Flex the cord near each plug while watching a circuit. An intermittent that follows the flex is a broken conductor inside the jacket, usually at the strain relief.
The Technology & Maintenance Council (TMC) of the American Trucking Associations publishes Recommended Practice RP 159, installation and inspection guidelines for seven-conductor truck–trailer and converter dolly jumper cable and connectors. Fleets that want a written inspection procedure should start there.
Common questions
Is the 7-way on a semi the same as the one on my pickup?
No. A semi-trailer uses the round-pin SAE J560 connector. Pickups and RVs use the flat-blade connector covered by SAE J2863. The circuit assignments differ for several colors, as shown above.
Why are the ground and ABS conductors heavier?
They carry more current. The ground returns every circuit on the trailer, and the ABS feeds power the modulator valves. J1067 cable sizes those conductors at 8 AWG and 10 AWG respectively.
Why is the ABS lamp on when the lights work?
Lamps work with only the lighting circuits intact. The trailer ABS needs constant power on the blue circuit and a clean ground, and its fault signal rides on that same circuit. A weak ground, corroded pin 7 or a cable without a continuous-power conductor can all trigger the lamp.
Can I rewire a J560 plug with any seven-conductor cable?
Use cable built to SAE J1067 or the vehicle maker's specification. General-purpose seven-conductor cable rarely has the heavier ground and ABS conductors, and its jacket may not survive the flexing and cold of a jumper cord.
What to send a supplier
- Connector standard (SAE J560) and whether you need primary, auxiliary or both.
- Cable standard (SAE J1067) and conductor sizes, plus jacket requirements such as cold flex and oil resistance.
- Straight or coiled, working length and lead lengths at each end (see coiled vs straight jumper cables).
- Plug style (molded, zinc die-cast or other), sealing and strain relief requirements.
- Test requirements: continuity and pin-to-circuit verification on every cable.
For the rest of the trailer harness, see trailer wiring harnesses and 7-way cables.
Last reviewed 2026-09-17