How does the Mazda RX-7 FD ignition system work and where can I find a simplified wiring diagram?

Difficulty: Moderate (for diagnosing and probing ignition signals)

Understanding the FD RX-7 ignition system is straightforward once you break down the wiring. It operates similarly to other vehicles of its era, relying on the ECU to trigger an ignitor, which in turn charges and fires the ignition coils.

Here is exactly how the system works and how the wiring is laid out.

How the Ignition System Works

1. Trigger: When the ECU decides it wants to fire a coil, it sends a 5V signal to the ignitor, telling it to start charging the coil.
2. Charge: The ignitor receives this 5V signal and quickly switches a transistor ON, which connects one side of the ignition coil to ground. Because there is constant +12V power at the other side of the coil, current flows through it, charging it up and creating a magnetic field inside the coil.
3. Release: When the ECU wants to actually fire the coil, it stops sending the 5V signal and sends 0V instead.
4. Spark: The ignitor sees the 0V signal and turns its transistor OFF, stopping the charge. The magnetic field inside the ignition coil immediately collapses, which creates the high-voltage spark sent through the spark plug wires.

Wiring Color Breakdown

To trace this system, here are the wire colors you need to know:

• Light Green: This is the 0/5V trigger signal from the ECU to the ignitor. It sits at 0V most of the time and sends a short 5V pulse when the ECU tells the ignitor to charge the coil.
• Light Green / Black: This wire connects the ignitor to the coil. It sits at 12V most of the time and drops to a 0V pulse when the ignitor grounds the coil to charge it. Note: Mazda changes this wire color to Yellow / Blue in the ignition harness near the coils, so be aware of the color swap.
• Black / Red: This provides constant +12V power to all the ignition coils. It should always measure at least 12V when the ignition key is in the ON position.

Locating a Simplified Diagram

You can find a custom, simplified version of the factory wiring diagram that isolates just the ignition components and wire colors here: ¹.

Diagnostic Tips & Grounding

• Multimeter Settings: The pulses sent by the ECU and ignitor are incredibly fast (about 0.003 seconds). You will not be able to measure them using a standard multimeter in voltage mode. You must use a multimeter with a Frequency mode to read these signals ¹.
• Grounding: While the ignition coils themselves have plastic/rubber bodies that show zero conductivity and don't strictly require grounding directly to the engine block, your ignitor absolutely must be bolted to the chassis to function properly ¹.