Sounds like you have a short circuit, either in the PTO clutch, or in the wiring that goes to it. Inspect the wiring for any obvious spots where insulation has rubbed off or burned. Also look at the wiring at the back of the PTO engagement switch for these signs. Before buying an expensive PTO clutch, unplug its connector. Drive around with the PTO switch on (even though the PTO won't activate and the blades won't be engaged). If the fuse doesn't blow, the problem must be within the PTO clutch. If the fuse still blows, it must be in the PTO switch or the wiring from there to the clutch. Use an ohmmeter to trace and find the short. Good luck!