if i recall correctly, the ones i had was a kill switch using switch body to frame grounded connection when key is off and the start was a momentary contact switch across the other 2 pins to activate the starter solenoid after passing through an inline fuse
most of those 3 pin switches are on the pull start only oem setups and they use the 5 pin switches on the oem electric start models
well thats not good, trace the wires for a chaffed wire touching somewhere, thats the most common issue with blowing fuses
if the wiring looks ok, then it might be the starter shorted and drawing too many amps, or it could be the alternator ring under flywheel has something wrong causing the short