Greetings Luddite, Apologies for not replying earlier. If you go to the Gomog site and go to +8 specific , then Oil and Oil Pumps, then Pressure Isolator switch which leads you to Rover SD1 3500 Oil Pressure isolator Switch by Bill Beddows with a small imputes from myself. That should explain things. My 4/4 with a 45DCOE needs an electric fuel pump in the fuel line turned on by a switch just before starting to fill the float chamber. At the moment I unscrew the top hat on the DCOE and pour in a small amount of petrol when the car has not been used a while.
Doug
from deep deep downunder.