It may be a good time to drop the deck and have a look to see that everything is free to turn. Or at least roll the belt off the clutch and do the same thing. Let us know what you find. The tractor starts and runs on its own w/o jumpstarting- correct?

The deck has been removed, and yes it starts fine. Replaced the battery a few months ago. Now I've managed to rip the wires right off the pto. I'm guessing the thing started to free spin after I pulled the belt. Maybe I dislodged the groove from it's holder when removing the belt. How freely should the clutch spin when the mower is not running? I will note also that before I removed the belt, the voltage to the pto would start to jump to 12v as the blades started to spin, then fell to zero and nothing. Now that the wires are cut, I get solid voltage when I pull the switch?? I just figured the extra vibration was causing a bad connection to my meter (I don't have 'gator clips, just probe style) thought I'd mention it though.

OH NO!
You can e-mail me for a PDF manual covering tests and adjustments to the PTO clutch, though it might be too late unless there is enough of the wiring left intact on the PTO clutch for you to repair and reuse (or at least...repair and test).
Your symptoms sound like the PTO clutch might have a break in the wiring inside. This could be causing the the increased voltage that you note on the volt meter when the blades stopped spinning after you engaged the PTO. It would be normal for the voltage to drop in the PTO circuit when current was flowing all the way through the PTO coil wiring (because the wiring is carrying an electrical "load"), then when the supposed break in the wiring opened and no longer carried any current, the voltage would jump to a higher level on your volt meter (because the electrical load is gone now).
The fact that the PTO stops spinning the blades but you still show voltage in the PTO circuit says your PTO switch is good and the PTO clutch is bad.

I do think I can fix the wiring, and I want to test the clutch.

"I've managed to rip the wires right off the pto. I'm guessing the thing started to free spin after I pulled the belt. Maybe I dislodged the groove from it's holder when removing the belt. How freely should the clutch spin when the mower is not running?"

I think you have managed to disconnect the Anchor for the clutch housing OR the anchor has worn thru. The Anchor wearing thru would let the housing turn until only the wires were restraining it and they wore the insulation thru causing a short and causing the clutch to drop out.

There must be an Anchor to keep the housing from turning. When disengaged, there probably will be considerable resistance to the pulley turning as most for several years now have a brake to stop the blades from turning courtesy of your Federal Government.

I hope you have enough left to splice your wires, IF you find that the clutch is indeed kaput, I have a couple of new ones for $100 ea. plus shipping.

Walt Connerw
conner5 at verizon. net