Try looking for a problem at the switch and perhaps bypassing to see if you can get a start without blowing the fuse. Confirm machine in neutral.
Other culprit could be starter solenoid somehow failed. Might be easier to disconnect control wire from solenoid and turn switch and see if fuse blows. Solenoid (coil) could be shorted internally or to chassis ground.
Could be an interlock safety switch hiding in the start-control circuit gone bad either failed or wire somehow shorted to chassis--pinched, abraded.
Depending on age of machine and how maintained and stored (weather) I'd bet on switch followed by interlock then solenoid---especially if problem is sudden onset with no history (or a history: switch flaky or have to jiggle sometimes).
Probably need to break out the test light and / or multimeter to do some serious wire tracing. Using a wiring diagram would help--probably essential if not resolved quickly--troubleshoot.
You'll need a supply of fuses on hand or one of those aftermarket test fuses that is resettable---a "breaker"-type instead of a 'blow'-type.
Throughout process be aware and watch for 'hot' wires might draw a 12-v arc and either blow (other) fuses or hit something it shouldn't. It'll be a PiA but keep battery neg term disconnected between individual tests.
Be careful: once I unknowingly bumped the shifter into gear and got an unexpected start when jiggling an interlock wire and the durn thing jumped at me.
Keep us informed of progress and results, please.
/s/Stubb
