Power to the PTO clutch goes through the ignition switch
It is a circuit all by itself so if the fuse blows whenevr you energise the circuit there are only 2 items in there, the switch & the clutch
The switch is about $ 30 the clutch is about $ 300 .
In order to replace the drive belt you have to either remove the clutch or undo the wires that connect the clutch to the mower.
Funny enough there is a plug in this wire to facilitate it.
Some clutches have the plug built into the clutch , others have it in the middle of the wires that go from the clutch to the mower.
So you need to check the switch, the wire & the clutch.