Just checked grounds and voltage on the key switch. I was getting 12.65 volts at all positions on the switch required to start the engine, still not engaging the starter solenoid. Is there an east way to test the safety switches or could the time delay module have gone bad and caused the issue?
The method I use is to make some patch leads with male terminals on both ends after checking the solenoid by applying power to the trigger terminal and ground to the solenoid base.
This solenoid grounds through the metal base & on ZTR's a little moisture wicked in under these and no ground.
As a routine service technique I either grease the base before reinstalling or put some conducting paste around the mounting bolt
My patch leads are about 2" to 6" long and I use them to jump the switch plugs, stating with the key switch
So on your Ferris you pull the key plug & jump the red & yellow
Then one at a time jump each safety switch
When the engine cranks you have found the guilty party
If it still does not trigger the solenoid then I use longer leads to bypass the wiring between the switches
By virtue of the fact you mentioned you had tested the key switch terminals I assume you do have the circuit diagram for your mower .