I always use these FIAMM 72112 Freeway Blaster LOW Note Horn, which I have on both my 800re and cb500x ,
Depending on location sometimes a slight tweak on the bracket is required or use the standard bracket from your bike.
I buy them from my local motor parts store, just get the version with two spades as some come with a socket that fits more modern cars. These do not need anything doing to your wiring as long as the connections can reach, on my Honda I had to make two small tails with a male and female connecters but on the Suzuki I didn't
