M12 A-Coded Connector Pinout: 3-Pin, 4-Pin, and 5-Pin Wiring Explained

You know you need an A-coded M12 connector. But which pinout? The wiring for a 3-pin sensor is different from a 4-pin IO-Link device, which is different again from a 5-pin configuration. Get it wrong, and your sensor won’t power up — or worse, you’ll damage the device. Here are the standard pin assignments you’ll encounter in industrial automation.

Before you start: a note on standards

M12 A-coded connectors follow the pin assignment guidelines in IEC 61076-2-101. Most sensor and actuator manufacturers follow these conventions, but always check the device datasheet. Some manufacturers — especially on proprietary systems — use non-standard pinouts. When in doubt, the device manual overrides everything in this guide.

3-pin M12 A-coded: the simplest configuration

3-pin is the standard for basic switching sensors: inductive proximity switches, magnetic reed switches, and simple photoelectric sensors that only need to output one signal.

Notice that pin 2 is skipped. This is intentional — the 3-pin layout uses pins 1, 3, and 4 to maintain physical spacing and compatibility with 4-pin sockets. If you look at the face of a male 3-pin M12 connector, the pins form a triangular pattern, not a straight line.

Wire gauge for 3-pin A-coded cables is typically 22 AWG to 18 AWG. The current draw from a simple switching sensor is low, so the cable doesn’t need to be heavy.

4-pin M12 A-coded: the most common configuration

4-pin A-coded is what you’ll see on the majority of industrial sensors. It adds a second output or input, giving the sensor more capability without requiring a larger connector.

In a standard 4-pin PNP NO (normally open) sensor, pin 4 is the switching output. When the sensor detects its target, pin 4 goes high (+24V). If the sensor has a second output — for example, a photoelectric sensor with both light-on and dark-on outputs — that second output goes to pin 2.

Some manufacturers use pin 2 as an external input instead of an output. For example, a laser distance sensor might accept a teach-in signal on pin 2. Again, the device datasheet is the final authority.

5-pin M12 A-coded: IO-Link and multi-function sensors

5-pin A-coded is the standard for IO-Link devices and sensors that combine multiple functions — for instance, a sensor that outputs both an analog value and a switching signal through one connector.

In IO-Link mode, pin 4 becomes the C/Q line — bidirectional communication between the sensor and the IO-Link master. Pin 2 is often unused or used as an additional digital input. Pin 5 can serve as functional earth or as a third output, depending on the sensor design.

If you’re converting an older 4-pin sensor installation to IO-Link, the cable is physically compatible — both use the same M12 A-coded interface. But the IO-Link master needs the 5-pin connection to access the full functionality. A 4-pin cable in a 5-pin IO-Link system may still work for basic switching, but you’ll lose the IO-Link communication channel.

Quick reference: all three pinouts side by side

This table makes it clear: pin 1 (brown, +24V) and pin 3 (blue, 0V) are the same across all three configurations. If you’re troubleshooting a sensor that won’t power on, check those two pins first.

Female vs male: the pin positions are mirrored

This is a common cause of wiring errors. On a male connector (pins sticking out), pin 1 is at a specific clock position. On a female connector (sockets), pin 1 is at the mirrored position relative to the keyway.

When you’re assembling field-wireable M12 connectors, always refer to the diagram printed on the connector insert or the manufacturer’s datasheet. Don’t assume the pin positions are the same as the mating connector — they’re not.

How to confirm a pinout when the datasheet is unclear

If you have a sensor with an unknown M12 pinout and no documentation:

1. Identify pin 1 and pin 3 first. With a multimeter in continuity mode, check which pins connect to known power and ground on the device PCB if accessible. Otherwise, use a known-good M12 cable and trace wire colors.
2. Apply 24V to pin 1 (brown) and 0V to pin 3 (blue). The sensor should power up.
3. Test the output. Trigger the sensor and measure voltage between pin 4 (black) and pin 3 (blue). On a PNP sensor, it should go high when triggered.
4. Check pin 2 and pin 5 with an oscilloscope or multimeter if the sensor has additional functions.

If all else fails, contact the sensor manufacturer or the supplier who provided the cable assembly. A photo of the connector face with the pin numbering visible is often enough to get an answer.

M12 A-coded cable assemblies from NITAI Electronics

NITAI manufactures M12 A-coded connector cable assemblies in standard 3-pin, 4-pin, and 5-pin configurations. We supply:

• Male and female connectors, straight and angled
• Standard pin assignments per IEC 61076-2-101
• Custom pin assignments based on your wiring diagram
• PVC and PUR cable jackets, standard lengths 0.5m to 10m
• Shielded and unshielded options
• Samples available for testing before mass production

If you need a non-standard pinout — for example, a custom wiring for a proprietary sensor interface — we can build to your specification. Send us your pin assignment table or wiring diagram for quotation.

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