V3 MicroSquirt® - QuickStart Guide

Your coil's negative terminal can be used to send the engine speed signal (aka. "the tach signal") to your MicroSquirt® controller. However, you can ONLY do this if:

1. You are using your MicroSquirt® controller to adjust the fuel only (not ignition advance)
   *AND*
2. You do not have a CDI (capacitive discharge ignition) coil.

If you want to control ignition timing advance as well, you cannot use the coil's negative terminal for your engine speed signal (because the signal moves relative to the crankshaft position), so you must use a distributor, crank wheel, or cam wheel.

CDI coil terminal voltage is much too high for MicroSquirt® controllers. Instead, you may be able to use the tach output on the CDI box and not the coil itself.

If you are triggering directly off the non-CDI coil (instead of something like a missing tooth wheel or another relatively low-voltage signal), connect OPTOIN+ (Ampseal pin #30) to the coil's negative terminal, and connect the OPTOIN- (Ampseal pin #31) to a 12V source (rather than grounding it as some older instructions recommend).

This then uses the flyback spike off the non-CDI coil as a trigger (rather than the 12 Volt signal). Doing this reduces the energy dissipated in the circuit, prevent a thermal 'melt-down' of the components inside your MicroSquirt^® controller.