6-Pin AC CDI Wiring Diagram: Connections, Signals, and Ignition Circuit

6-Pin AC CDI Wiring Diagram: Connections, Signals, and Ignition Circuit — interactive diagram. Open it in the editor to customise components and wiring.

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A 6-pin AC CDI wiring diagram shows the connections between the stator AC source coil, trigger (pickup) coil, ignition coil, kill switch, and power supply on small engine ignition systems.

Capacitor Discharge Ignition (CDI) is the ignition system used on the majority of small petrol engines found in motorcycles, scooters, ATVs, outboard motors, and small power equipment. It replaces the contact-breaker points of older systems with electronic switching, providing faster, more reliable spark delivery.

AC CDI (also called source-coil CDI or magneto CDI) is the most common variant on basic small engines. The 'AC' refers to the power source: the CDI unit charges its internal capacitor directly from an alternating current generated by a dedicated exciter or source coil wound on the engine's magneto/flywheel stator. No battery is required for the ignition function itself, making AC CDI systems lightweight and ideal for entry-level motorcycles and small utility engines.

On a typical 6-pin AC CDI connector, the pins serve the following general functions (note: pin assignments vary between manufacturers and models — always consult the specific vehicle service manual):

Pin 1 — AC input from the stator source/exciter coil. This supplies the alternating voltage that charges the CDI's internal capacitor. At cranking speed, this voltage is typically 100–200 V AC peak.

Pin 2 — Trigger/pickup coil positive signal. This is the pulse signal from the magnetic pickup coil (also called the pulse coil or trigger coil) mounted on the stator, which detects the flywheel trigger tab and sends a timing pulse to the CDI to release the stored capacitor charge.

Pin 3 — Trigger/pickup coil negative (reference/return).

Pin 4 — Ignition coil primary output. When triggered, the CDI discharges its capacitor through this terminal into the primary winding of the ignition coil, inducing the high-voltage secondary spark.

Pin 5 — Kill switch input (ground kill). When the kill switch is closed (engine stop activated), this pin is grounded, preventing the CDI from discharging and killing the ignition.

Pin 6 — Ground.

This description is generic and illustrative. Pin counts and assignments differ across manufacturers. Always verify against the specific machine's wiring diagram.

How to wire 6 pin cdi wiring diagram

Obtain the vehicle-specific wiring diagram Before testing any AC CDI circuit, obtain the wiring diagram for the specific make and model. Pin assignments on 6-pin CDI connectors vary between manufacturers. Do not assume pin functions from this generic description alone.
Test the stator exciter coil output Set a multimeter to AC voltage. Disconnect the CDI connector. Crank the engine by kick-starting or pressing the electric starter. Measure across the exciter coil output wires. A healthy exciter coil should produce at least 80–100 V AC at cranking speed. Low or zero voltage indicates a faulty exciter coil or poor connection.
Test the trigger (pickup) coil resistance With the CDI disconnected and engine stopped, measure resistance across the trigger coil terminals. Compare against the manufacturer's specified range (commonly 50–500 ohms depending on the engine). An open reading (infinite) or a short (near zero) indicates a failed trigger coil.
Test the ignition coil primary resistance Measure resistance across the ignition coil's primary terminals (the low-voltage side, connected to the CDI output and ground). Typical primary resistance is 0.3–1.5 ohms. An open reading indicates a failed primary winding; check the secondary winding (spark plug cap to coil body) — typically 5 000–15 000 ohms.
Check the kill switch circuit With the CDI connected and engine cranking, operate the kill switch in both positions while checking for spark at the plug. If the engine will not start at all, temporarily disconnect the kill switch wire from the CDI and attempt to start. If it then starts, the kill switch or its wiring is shorted to ground.
Inspect the CDI connector and wiring Corrosion, bent pins, and cracked insulation are common CDI faults that mimic a failed CDI unit. Clean corroded connector pins with electrical contact cleaner, check for cracked insulation on the stator wires (which pass through the engine's inner cover and are prone to abrasion), and verify all pins seat fully in the connector body.

Specifications

Exciter coil output voltage (at cranking speed)	Typically 80–200 V AC peak (varies by stator design and cranking speed)
Trigger coil resistance (typical range)	50–500 ohms (verify against vehicle service manual)
CDI internal capacitor charge voltage (typical)	200–400 V DC (internal; not accessible for safe measurement)
Ignition coil primary resistance (typical)	0.3–1.5 ohms
Ignition coil secondary resistance (typical)	5 000–15 000 ohms
Secondary ignition voltage output (typical)	10 000–40 000 V AC (varies by coil and CDI design)
Operating temperature range (CDI unit, typical)	−20 °C to +85 °C
Pin count	6 (this variant); AC CDI systems also exist in 4-pin and 5-pin configurations depending on application

Safety warnings

CDI systems generate high-voltage discharges (10 000–40 000 V AC) at the ignition coil secondary. Never touch the spark plug cap, HT lead, or ignition coil tower while the engine is cranking or running. High-voltage ignition shock is painful and potentially dangerous.
The stator exciter coil produces over 100 V AC during cranking — sufficient for a significant shock. Do not probe exciter coil wires while cranking the engine with bare fingers on the probes. Use properly insulated multimeter probes.
Disconnect the spark plug lead and ground it to the engine before performing CDI bench tests involving cranking the engine without attempting to start it, to prevent accidental starts during diagnostic work.
Keep hands clear of moving parts (kick-starter mechanism, flywheel cooling fan, chain/belt drive) when cranking the engine for testing.

Tools needed

Digital multimeter (AC voltage, resistance modes)
Inline spark tester (for verifying spark presence without removing spark plug)
Spark plug socket and ratchet
Electrical contact cleaner spray
Vehicle/equipment service manual with specific wiring diagram
Oscilloscope (optional; for viewing trigger coil pulse waveform)

Common mistakes

Replacing the CDI unit before thoroughly testing the stator exciter coil and trigger coil — a failed stator is more commonly the cause of no-spark than a failed CDI.
Installing a non-application-specific CDI based on identical connector shape, which may have different timing or trigger polarity characteristics.
Grounding or shorting the trigger coil signal wire during diagnosis, which can damage the CDI's thyristor input.
Neglecting to inspect stator wiring for chafing against the engine case — stator wires are routed through a hole in the engine cover and are a common failure point on high-vibration small engines.
Using a non-resistor spark plug in a CDI ignition system — CDI systems often require resistor-type plugs to suppress radio frequency interference; non-resistor plugs can cause ignition module interference and misfires.

Troubleshooting

No spark at all, engine will not start: Cause: Failed exciter coil, failed trigger coil, open CDI kill circuit shorted to ground, failed CDI unit, or failed ignition coil Fix: Follow the diagnostic sequence: (1) verify exciter coil AC output during cranking; (2) verify trigger coil resistance; (3) temporarily disconnect kill switch circuit; (4) verify ignition coil winding resistances; (5) substitute a known-good CDI as the final step.
Spark present but engine will not start or runs poorly: Cause: Ignition timing incorrect (wrong CDI for engine, or incorrect flywheel key alignment), weak spark from failing CDI, or incorrect spark plug Fix: Verify the CDI is the correct application-specific unit. Check flywheel key is not sheared (a common fault after the engine kicks back). Verify spark plug type and condition. Measure secondary coil resistance.
Engine starts but dies when hot: Cause: Heat-sensitive failure in CDI unit, stator coil, or ignition coil — common as insulation degrades with age Fix: Allow the engine to reach operating temperature, then immediately perform the same exciter coil output and trigger coil resistance tests as for a no-start condition. A component showing normal cold resistance but open or high resistance when hot is the cause.

Frequently asked questions

What is the difference between AC CDI and DC CDI?

An AC CDI charges its internal capacitor from an alternating current generated by the engine's stator exciter coil — no battery is needed for ignition. A DC CDI charges its capacitor from the vehicle's DC battery via an internal inverter/boost circuit. AC CDI systems are simpler and work without a battery; DC CDI depends on battery voltage and is common on vehicles with electric start systems.

How does a CDI unit produce a spark?

The CDI charges an internal capacitor (typically to 200–400 V). When the trigger coil detects the flywheel's timing mark, it sends a small pulse to a thyristor (SCR) inside the CDI. The SCR fires, rapidly discharging the capacitor through the primary winding of the ignition coil, inducing a high-voltage pulse (10 000–40 000 V) in the secondary winding, which fires the spark plug.

How do I test a CDI unit?

CDI units are difficult to test accurately with a standard multimeter because they operate at high voltages and fast switching speeds. A basic bench test: verify AC voltage output from the stator exciter coil at cranking speed (typically 80–200 V AC). Verify trigger coil resistance (typically 50–500 ohms) and AC output pulse. If source voltage and trigger signals are present but no spark occurs, the CDI unit is suspect.

Can I replace a 6-pin AC CDI with any 6-pin unit?

No. Physical connector similarity does not mean electrical compatibility. CDI units differ in capacitor voltage, trigger signal polarity, timing advance characteristics, and pin assignments. Fitting an incompatible CDI can result in no spark, incorrect timing, or damage. Source a replacement specified for your exact make, model, and year of engine.

Why does my engine die when I release the kill switch?

On many AC CDI systems, the kill switch grounds the CDI to stop the engine. A kill switch or wiring fault that grounds the kill circuit continuously will prevent the engine from running. If the engine dies immediately after starting, check the kill switch circuit for a short to ground — a pinched wire contacting the frame is a common cause.

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