The windscreen wiper switch, which has an integral pump for the washer, has been replaced with a generic two stage single pole switch. The second stage is meant to run an electric washer pump but has failed.
An old good switch with pump has been obtained.
My concern was that the rosette. or securing nut. used on the generic switch would not be compatible.
But the actual problem is that the knob is too large for the switch spindle.
Now, the parts list only shows one switch part number, and thus one spindle size. But, on closer inspection it shows several knobs (hard and soft finish) with notes which indicate they have two thread sizes, M3.5 and M5. How two different size knobs are meant to fit one spindle size I don’t know.
So, either the knob has been bored out to fit the generic switch, or it is the larger size from the parts list.
Either way, an adaptation is now required.
Another simple job turned complex!
All sorted now using the original switch and a separate descrete washer switch.