Leon, on the G1900, the Engine Stop Solenoid does not work as you described. What happens is that the ignition key being turned to OFF sends a signal to the Combination Box. With this signal the combination box then sends 12 volts to the Engine Stop Solenoid for 8 seconds. The solenoid energizes and moves the fuel injection pump rack to the "No Fuel Position" so that the engine then stops. After 8 seconds, the solenoid is de-energized and the rack returns to its normal position, ready for the next time the engine is started.
This is quite different from normal fuel cutoff solenoid operation on other diesels. To test the solenoid, I would jumper 12 vdc to it to see if it operates. I would then monitor the voltage coming to it from the combination box and turn the key to off to see if the 8 second signal was being sent properly by the combination box relays. If joa4444 does this, he will know if he needs a solenoid or a combination box. Many people just hook up a mechanical link to the rack with a pull knob so they can kill the engine without all this complicated timing. My G1800 is that way and all I do is turn off the key and pull the knob to kill the engine. Works great!