I've had similar experiences with my 99 model Grasshopper. The first time it was caused by the pto switch. The next time it was the plug to the electric clutch. Exposure to dirt and corrosion over time causes the failure. Pretty easy to trouble shoot even without a schematic. I would do a visual inspection of the connections at both the switch and clutch. If those look good, check for continuity of the clutch and for voltage to the clutch. Check continuity with the clutch disconnected. The mower doesn't have to be running to check for voltage. With the clutch plugged in and the pto switch "on", you should hear the clutch click when you switch the ignition switch "on". Of course the clutch could be slipping, which will likely require replacement. Some of the older clutches had three studs with nuts that are adjustable.
Good luck.
Jim
