I found my oil pressure switch (in the pic bottom right)
when I was digging out the handlebar switches for my handlebar master cylinder
that I am going to rebuild with the 'rebuild kit'
that has just arrived from Cyclehaven
along with an Oil Pressure Switch for the oil pump
(sealing that hole from debris) that Rowan kindly gave me some advice on.
I'm hoping to run just one switch housing on the bars,
keeping just a clutch lever on the left.