Since you have 3 OPR's (Operator Presence Relay) I'd unplug all of them.
Also, put the key in the RUN w/o lights position to eliminate the head light circuit.
Does it still blow the fuse?
Try this with the seat unoccupied first. IF it doesn't blow, occupy the seat and see if it does/does not.
IF still no blown fuse, put switch in headlights ON position. IF it blows, it's in the head light circuit.
IF not blown, substitute each OPR back in, one at a time.

I have a hunch OPR 2 and/or 3 may be involved, which would involve the alternator/Voltage Regulator.

This post was edited by bill_kapaun on Wed, May 14, 14 at 10:54

Have you delved into the owner's manual for your mower?
In the manual, the Protection Loop (part 141940) seems to be indicated as an "either/or" type item in the hour meter circuit.
So, it may be that either the tractor has an hour meter, or it has the Protection Loop.
I see no correlation at all between the Protection loop and the ammeter.
Does the fuse blow when the key switch is in both operating positions (RUN + LIGHTS and RUN - NO LIGHT)?
This problem you describe (suddenly blowing fuses) has appeared in the forum in the past, but if I recall correctly, there were reasons other than a protection loop component involved in those failures.
Watching the video you linked to made smile when the guy walked from the Kohler powered tractor over to the Briggs powered tractor and pointed to "a diode" used on that tractor. The diode he pointed out on the Briggs is the OEM Briggs rectifying diode for the Briggs 3 amp charging system, no relation to anything regarding a protection loop.
And looking at the owner's manual for your tractor, I see that it has the Kohler 15 amp alternator charging system.
I then referred to the Kohler service manual and the 15 amp system used on CV 16's has a combo rectifier/voltage regulator instead of having any separate diodes, or in other words.......the diodes are "built into" the regulator module.

So, if I was trying to find the culprit, I would be checking out the key switch first to determine if it had suffered an internal failure that is allowing the Battery Positive feed circuit to short to ground inside the switch.
The key switch is comprised of both battery hot circuits and is also equipped with a grounding circuit.
I have seen numerous cases of key switches failing internally with the symptoms you report.
If it was me doing the testing, I would pull the multi wire connector loose from the key switch and use a jumper wire to jump from the battery hot terminal (RED wire that is hot) in the connector (marked B on the switch) over to terminal A1 in the connector. Making that jump duplicates the action of turning the key to the run position. If you are able to jump between the B wire and the A1 wire without the fuse blowing......replace the key switch.

This post was edited by mownie on Wed, May 14, 14 at 11:56

Thanks for the quick responses, guys. You are both tremendous assets to this forum. I followed Bill's advice and after unplugging the the 3 OPs and headlight circuit, it cranked right up. So I replugged, one at a time, testing each time, no problem. Then I hit the seat switch. Ding ding ding! Seems one of the seat switch wires decided to commit suicide by jumping out of the protective sleeve, right where it passes between the battery holder and the frame. There she was, a pinched exposed wire, giving me that intermittent short when I sat/pressed the seat. Thanks again for your quick responses!

That's good to learn. (that the problem spot was found).
And had you tried my method (regarding the use of a jumper wire on the key switch connector) it would have disclosed that the shorting condition still existed. But it would have exonerated the key switch.