Adrian, If your bike has the diver's helmet, you may find the switch knob tail fouls on the cowl where the pressing turns out to cover the fork shroud. I am led to believe the switch comes as a short or long knob type.
I didn't know this long ago, and just cut away one of the switch locating tabs on the cowl, to turn the switch body slightly. Not noticed, but it would have been better in retrospect to obtain the correct knob. That was then, now you are spoilt for choice.
A thin rubber ring goes between the underside of the switch and the cowl. Julian's picture shows the clip, which engages in slots moulded into the switch body parallel to the switch face.
Swarfy.