I have recently installed one of these on my 1100. I opted for a split installation given the limited space under the plastic. There is plenty of instruction on how to separate the compressor from the trumpet via google so I will not go into that here. After doing a bit of research the opinion of most is that there are really only two spots on an ST1100 to mount this horn. One spot being in front of the right fairing pocket and the second being behind the left tip over wing. I found a bit about the possibility of mounting this horn around the spot where the OEM horn sits however those who have tried seemed to think that cutting the plastic would be necessary for this. Thought I would take up the challenge and try and make it work. Happy to say that the horn can be mounted in this space without chopping anything on the bike. It is just a but of fiddling to make it work.
Once the horn is separated the first step was to remove the plastic. I used hose clamps to mount the compressor to the frame behind the left tip over wing.
Wiring is straight forward. Although most people suggest not to use the stock relay I opted to use this. I figure I can always replace it easily enough should it fail. I used cable ties to mount the relay.
I then ran a hose between the compressor and the trumpet. The trumpet is also held on with a cable tie however sits on top of the innrer fairing panel beside the front wheel nicely. The trick to make it fit is to get rid of the wings on the trumpet that originally gripped the compressor right down to their bases.
I have since replaced the clear hose with a stainless steel covered fuel line for heat resistance. Should have realised that clear plastic thing would melt. So much for common sense :)
The last image shows the trumpet fully enclosed. The trumpet openings are outward against the plastic and reasonably protected from water entering. It sounds super loud compared to the stock horn and very much worth the effort to get it on.
