There's lots in here already on the Nautilus compact - there's also a version that's split into two parts to make it easier to mount on the Old Pig. Some folks have had succeess by placing in the Goldwing unit in place of the Beemer's rather sucky stock unit.
We've all probably hit the horn to wake up some dumb ass, half asleep driver, only to wither at the measly wimper, the stock unit squeeks out
Won't be long till someone kicks you in the shins and asks you to use the search function (a culture thing round here - don't take it personally)
If you try the search function and put the little +sign right in front of terms like +stebel +compact ..... and even +harness, you'll be reading about horns - and how to mount them to the GS for about three hours.
good luck - and please come back tell us what you found out,
cheers - Bull