I have a 2012 SYM Fiddle II and when I turn the key on to start the scooter, the horn starts blaring. It will continue blaring when you are riding it too. How can I fix this?

Your horn button is defective. It is touching ground all the time completing the circuit and blowing the horn. If the wire going to the horn is frayed and tiucjing metal anywhere that is the same as the button which connects the wire going to the button to metal on the bike also known as ground. Find what color the wire is by looking at the horn itself. One side of the horn is battery plus voltage. The other side when grounded makes the horn blow. Unplug it if you can't solve it.