oil pressure sensor 75 TS ???

[mattstead]

Hi there, the oil pressure guage on my 75TS doesn't seem to work, although the oil warning light does. I wanted to check the pressure sensor but to be honest don't know where to look.
As I stand at the front of the car looking in the engine bay I've found an oil pressure switch with a single contact (so this can't do pressure can it?) down on the right, and I've found a double contact electronic dip stick kind of thing on the left.

Is it either of these, or is there something else? is this a common fault? what is it normally? clocks? wiring? etc, etc.

Many thanks for any help.