Genie S40 emergency stop does not work

I have recently purchased a 1998 Genie S40 boom lift. Duel fuel (gas/lpg) with about 4K hours and change. Upon purchase, the seller did mention that they had rewired the fuel pump to stop providing power when the key switch or emergency stop was activated. The engine does not stop until the carburetor runs out of fuel. I got the service manual and studied the electrical diagram in detail. My problem is either the ISM (Ignition Start Module) or some wiring issue. I used my multimeter and verified that the key switch and emergency cut-off switch cut power going out of the switches. However, power is not cut to the ISM since there is a wire that goes straight from the battery to ISM (pin 20 on the service panel and then pin 6 on ISM) - there is a constant 12v at those locations at all times and the schematic diagram confirm that. My question is when I cut power from the emergency switch what triggers an immediate shutdown of the engine? My suspicion is that when power is cut, ISM pin 9 which provides the ignition power should be cut off but it does not - a trigger should initiate the shutdown but I am simply not seeing it. Pin 7 and 8 according to the schematic are connected together which they are. Any ideas would be appreciated - I have spent and learned quite a bit the last couple of weekends but I am running out of ideas on debugging this. Thank you! Steve