Thanks Ian, very helpful. I'm familiar with electronic systems such as Bragg Cells or Piezo electric semiconductor systems that have variable optical outputs commensurate with pressure, but couldn't imagine anything "lower tech" that would work to create variable electric output. I'd never have considered a pile of carbon discs!

In my Daimler 15 there is a copper pipe from the oil system that connects to an oil pressure gauge on the dashboard - can anyone explain the principle of operation within the pressure gauge please?

Mechanical oil pressure gauges are usually of the Bourdon tube type. The video below explains the operation.

Hi Dave, interesting discussion and it took my thoughts to my 37 Muliner 15 which as you will know for some strange reason has it's oil pressure gauge under the bonnet fitted to the oil filter casting. Never could understand the logic in it's position.

When I got the car, the engine was and still is covered in gunge and I discovered the gauge whilst cleaning the gunge away from the oil filter bracket to change the filter, could not have been read for years.

Happy 2019 to you and yours. Syd