[bestgenman]

I’m addressing what I think you are asking for.  
The isochronous governor is a steady state speed control regardless of load.  Most of our sets are droop governed.   There are three components to make up the system.  
1. Mag pickup.  Senses speed by counting the teeth on the flywheel generally. Generates a somewhat square wave.
2. Speed controller.  This receives the pickup signal , has power (12vdc), and converts to an output which feeds the actuator.  The signal is generally PWM (pulse width modulated). There are gurus here that can explain that better than I can.
3. The actuator.  It appears, on these engines, attached to the injection pump resembling the shut down/run solenoid.  It moves the fuel rack inside the pump adjusting fuel delivery in accordance with speed.

The common downfall is actuator sticking.  This causes erratic speed or no speed at all mostly. The fix is , replace the actuator.  Occasionally, the controller fails and this almost always results in no signal to the actuator.

Hope this is what you were looking for.  If not, I’ll take another stab at it!