My 2002 Plus 8 had a separate oil pressure sender just for the gauge. I had to replace it as the gauge became erratic. It's a pressure switch wired to the gauge, screws into the engine block rear. Two wires onto spade connectors. Easy to replace. Bought replacement from Melvyn Rutter, not expensive ( for a Morgan). A quick change whilst underneath and car on stands. Access good.
Seeing the gauge become erratic was not pleasant! The ecu would stop the engine if no oil pressure based on a sensor elsewhere ( oil pump I think from memory). Oil pressure on a Rover V8 was not high anyway. Seeing the gauge drop at idle speed was normal but took some getting used to!
