The Stebel Magnum is a good horn, but try and place it in a way water can't get in, or it won't be loud when you need it most.....don't ask me how I know!
I've just come in after fitting a magnum.Went in the garage full of hope & had a look.Bollocks, it ain't a straight swap.Had to cut the BMW plug off & connect some spade connectors to the wires & THEN it was straightforward.By the way take a good light, it's dark under there.Good horn though & I think it's the low note.(bike is a 2002 1150 so check your connections first so you can get a couple of spade connectors before you begin !)