Adam, the manual has a series of diagnostic steps that are too long to re-type here.
I was less clear than I should have been in my previous question: do you have 12V at the PTO solenoid itself, with the PTO switch on, you in the seat, engine running? From the manual, it looks like a blue wire from the PTO switch goes to a connector that joins to a white wire at the solenoid. Remove that connector and check for 12V on the blue wire.
If you do have 12V to the solenoid when you should, I think it takes all the wiring out of the question, and you should be looking for an electrical problem in the solenoid itself, or a mechanical or hydraulic problem with the clutch. Check the solenoid resistance as the next step - it should be very close to 0, no more than 0.1 ohms.
Tim