The same thing happened to me a couple of years ago after I was doing brush work. I would check under tractor at the rear- there are a couple of bullet type wiring connectors under the left fender that can come apart. My experence with those is, if they come apart while running it stays running till turned off then it won't restart. I found that some branch had caused the disconnect. The #2 fuse has been the bane of existence for many TC owners. I always check it even though I installed a circuit breaker fuse. What you did with the hot wire ruled out the seat safety relay switch. The neutral safety relay is under the left fender, its possible that the "contact lever/rod" (my descriptor) overran the contact switch on the relay. The only other safety relay I can think of is the emergency brake relay- does your parking brake light go on? I have to add that I am no mechanic; but I have had a few problems with safety relays on occassion. I have had my dealer do a "house call" once for one of my safety relay problems. You appear much better at mechanics than I, but I hope this helped to some degree.