Oil pressure switch/sender

[stedale]

A really simple question that has probably been asked a zillion times before (I searched but could not find):

How do you test a Oil low-pressure switch that you suspect to be duff? All I know is the oil light doesn't light on startup and it's not the bulb that is broken.

Thanks in advance,

Steve.

[grahambell]

The pressure switch is designed to break the circuit under pressure. With no pressure the circuit is complete, being earthed through the engine, so take the lead off the switch and try earthing the contact directly to the engine or other suitable metal part (or even the battery - terminal). If the wiring's OK the buld should light (with ignition on of course) indicating that switch is at fault.

If bulb doesn't light, then assuming you have a good contact, there could be a fault in the wiring.

[stedale]

Excellent, thanks for your reply - it seems obvious to me now it's been explained!

Cheers,

Steve.

[grahambell]

Happy to help.

The other alternative if you have an electronic test meter is to measure the resistance (Ohms) between the body of the switch and its sender lead contact terminal. With engine off and no oil pressure you should have a complete circuit and so no resistance (0 Ohms) whereas if you're actually getting infinite Ohms then you have an open circuit and a duff switch.