Oil pressure warning light

[B92 8NW]

D1 300Tdi.

Oil pres. warning light doesn't come on with the ignition anymore, except sometimes first thing in the morning.

I'm guessing the sender needs replacing. How do I test the circuit? Do I ground the wire or connect power to it?

Any other reasons to explain why it only sometimes comes on with the ignition?

[JDNSW]

If it is only the oil pressure light it is probably the sender. Check this by earthing the lead to the sender - should switch on the light. The other, less likely possibility is a wiring fault.

John