BMC A Series oil warning light

You're very trusting driving the car with the oil pressure light on. Not something I'd do - unless it also has an oil pressure gauge showing things are OK.

Does it have a modern spin-on filter (which will have a clogged bypass valve) or the original canister variety?

In message , "Dave Plowman (News)" writes

Trusting, up to a point. Having removed the wire from the pressure sender, and the light remaining on, I have proved that it is not the pressure switch powering the warning light. I suppose it is possible that the warning light would be on even with the wiring fault fixed.

(Thinking aloud) If I run a wire direct from the battery to a 12v bulb, then to the pressure switch, the bulb will light. Then running the engine *should* extinguish the bulb, which will prove the oil pressure is OK. I think.

Are we sure that this light is not operated by a relay of some kind, rather than by the sensor directly? Brian

In message , Graeme writes

Answering my own question, I have just tried a test lamp between the battery and oil pressure switch. With the engine not running, the bulb lights. Start the engine, and the bulb extinguishes, as expected (or hoped!).

The fault must be a leak to earth, almost certainly behind the speedo, which is a bit of a nightmare to access, due to the heater which is directly below the speedo.

In message , Brian-Gaff writes

Brian, no, nothing so sophisticated. This is a 1968 Morris Traveller, and the wiring for the oil pressure warning light runs from the ignition to the bulb, then to the sensor for earth, with a fuse in circuit.

Unless you've had mice ;-) the most likely thing is it has frayed going through the bulkhead, etc. But car electrics are odd things - have a habit of defying logic.