Most likely during your install of the parts you shorted a circuit. You should buy a 12Vdc circuit (power / logic) probe and a digital multimeter. You can buy them from Harbor Freight rather cheaply and in this thread I show you the ones a non professional mechanic should own.
http://www.scootdawg.net/showthread....467#post534467
If the main fuse is blowing, it tells you that you are pulling too much power through it and it burns out to protect the circuit. That cheap meter can handle up to 10 amps flowing in a circuit before its internal protection (fuse) blows.
Go to the local auto parts store, buy a cheap inline ATO or ATC fuse holder, get some low amp fuses like 5 amp (cause you will burn out a bunch of them). Connect the inline holder across where the original fuse goes, disconnect the scooter ign switch, stator and regulator, then install a fuse in the new holder--
Did it burn out right away?