The internal Honda ignition module (ignitor) can be bypassed or replaced with a solid-state circuit to provide a clean trigger signal for aftermarket ignition boxes, such as MSD or Crane systems.

Overview#

This modification allows the ECU to trigger an external ignition controller directly, bypassing the high-current switching requirements of the factory ignitor.

Note

The ZTX857 transistor is not a strict requirement. Any NPN Darlington power transistor capable of handling the necessary current load can be used as a substitute.

Circuit Diagram#

Schematic for solid-state ignitor replacement

Implementation Details#

To interface the Honda ECU signal with an aftermarket ignition box:

1. Transistor Selection: Ensure the chosen NPN Darlington transistor is rated for the current requirements of the ignition trigger input.
2. Wiring: Connect the circuit according to the schematic above, ensuring proper grounding to the distributor housing or chassis to prevent signal noise.
3. Compatibility: This setup is compatible with most capacitive discharge ignition (CDI) systems that accept a standard square-wave trigger signal.

Warning

Ensure all connections are soldered and heat-shrunk to prevent vibration-induced failure within the distributor environment. Improper wiring may result in a no-start condition or damage to the ECU ignition output stage.