Hi I have had this one out with the guys from our local dealer whom I am very friendly with.
The switch you fit with the pedal up and you twist until located and give a further twist which if you look carefully at the switch you will see a small green tab, this must be protruding indicating the switch has been fitted correctly. I have been told that if the tab doesn't protrude then the switch will give trouble and malfunction often bringing on the EML light. We have very little trouble with these switches, and we only fit the genuine switch as it switches more than just the brake lights. John Kennard