I am not a lover of alarms - believing an immobiliser and quality chain works just as well - and there are so many reports of batteries draining and upsetting the neighbours with a false trigger.
I am picking up a Speed Twin which has an S4 version, and even the guy selling it recommends that it be removed!
So. Looking around it does seem fairly straight forward with some good videos.
The S4 looks like unplugging the white socket from the Triumph loom and cutting all the wires from the alarm side of this socket, and then shorting terminals 1 & 2, and 3 & 5, before reconnecting the plug back into the loom.
I would assume the alarm is set to Winter or some such before starting!
Of course, if cutting/shorting wires is not your cup of tea, you can buy a replacement plug already made up for around £20...
There is also a video of disabling an S3 version, which seems to be slightly different.
Hope this may help. Let me know if you would like the video links...
