Editing Openai/69540633-2650-8006-9f7f-3526b70a3503 (section)

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* A CKP sensor reads a reluctor wheel on the crankshaft
* Produces an AC waveform
* ECU uses this for: - Engine speed - Crank position - Spark timing reference

⚠️ If CKP is missing → NO SPARK, NO INJECTORS

===== Once ECU sees: =====
* Valid CKP signal
* Correct system voltage
* Safety inputs satisfied

It will:
* Calculate ignition timing
* Control coil dwell time
* Fire coils independently

===== Each ignition coil has: =====
* Battery power (Key ON / RUN)
* ECU-controlled ground (driver circuit)

Operation:
* ECU grounds the coil primary → current builds (dwell)
* ECU opens the ground → magnetic field collapses
* Spark occurs

This is exactly like an automotive COP system, just simpler.

===== Scag does NOT kill spark directly. =====

Instead, safety switches feed inputs that:
* Enable or disable ECU operation
* Allow or prevent fuel + spark

Common inputs:
* Seat switch
* PTO switch
* Brake switch
* Neutral switch

⚠️ A failed safety input can cause crank/no-start with no spark, even though power and grounds look good.