Many thanks for this. Finally got round to doing it. Purchased a pushbutton switch. Carefully parted the old plastic top from existing switch. Bent up a piece of aluminum. Mounted pushbutton switch on it and Carefully pop riveted bracket to existing casing. That bit done I purchased an electric screenwash pump. Eventually got to fit that and then a bit of wiring. All done and works a treat. Shame water bottle is not bigger as can imagine might empty quicker. It's a lovely conversion and keeps the original switch.