Oil Pressure Warning Light conundrum

I have a 2003 Defender TD5, 92k miles, runs sweet as a nut.
This week the oil light came on, and stayed on. Checked the oil, full. No nasty engine noises.
I was suspicious that this wasn't actually an oil pressure problem, so connected a pressure gauge (which was last calibrated July this year) and started the engine. On idle, cold, was 45 psi. On increasing the revs a bit the pressure went up to 50, 55 then 60 psi as the revs increased. I didn't take it any further than that as the pressure looks ok to me and compares well with the spec in the workshop manual. So, the oil pressure was ok......
I bought a new oil pressure switch (correct LR/Lucas part) and fitted it, to try to eliminate that from the equation. This did not solve the problem, as:
- the oil warning light came on when the ignition was switched on (engine not started) but went off a couple of seconds later.
- I pulled off the connector from the oil pressure switch and tried again. Same result; the oil warning light came on when the ignition was switched on (engine not started) but went off a couple of seconds later.
I checked the continuity of the wire that runs from the connector behind the instrument panel to the connector on the oil pressure switch and it buzzed out ok.
So, I have an engine with bags of oil pressure but an oil warning light that is pretty useless.
Has anyone else had this problem? Would be very pleased to receive your advice as I am now a bit stumped.

oldapprentice said:

I have a 2003 Defender TD5, 92k miles, runs sweet as a nut.
This week the oil light came on, and stayed on. Checked the oil, full. No nasty engine noises.
I was suspicious that this wasn't actually an oil pressure problem, so connected a pressure gauge (which was last calibrated July this year) and started the engine. On idle, cold, was 45 psi. On increasing the revs a bit the pressure went up to 50, 55 then 60 psi as the revs increased. I didn't take it any further than that as the pressure looks ok to me and compares well with the spec in the workshop manual. So, the oil pressure was ok......
I bought a new oil pressure switch (correct LR/Lucas part) and fitted it, to try to eliminate that from the equation. This did not solve the problem, as:
1- the oil warning light came on when the ignition was switched on (engine not started) but went off a couple of seconds later.
2- I pulled off the connector from the oil pressure switch and tried again. Same result; the oil warning light came on when the ignition was switched on (engine not started) but went off a couple of seconds later.
I checked the continuity of the wire that runs from the connector behind the instrument panel to the connector on the oil pressure switch and it buzzed out ok.
So, I have an engine with bags of oil pressure but an oil warning light that is pretty useless.
Has anyone else had this problem? Would be very pleased to receive your advice as I am now a bit stumped.

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Stage 1 and 2 with engine not started is caused by the systems self check.......just make me understand...after that if u start the engine the warning light comes back and no other lamps illuminated? .if yes.....U have to check the diagram to see with which other bulbs is the oil warning lamp connected on self check......the oil lamp is not supposed to go off untill the switch "feels" the oil pressure form the working engine. .......unfortunatelly i dont have Defender diagrams just Disco 2 to look.

Update: (i erased the bollox from my previous message)........ unplug the connector from the switch and check if u have earth on it(with ignition off then on).......if yes then we are getting closer coz it's not supposed to be there, if not check the pin from the connector behind the dash.....also doesnt have to be earth.....the fact is that if the oil lamp illuminates with the switch unplugged that means it gets a false earth from somewhere else. the switch is supposed to supply earth to the lamp through its normally closed contact then when oil pressure kicks in the contact opens and the lamp goes off......i think its a kind of strange short circuit and the oil lamp is working in parallel with an other warning lamp meanwhile the other warning lamp which is connected to the oil lamp doesnt work.......:doh::frusty::suspicious:....fookin eldritch. If u are familiar with diagrams check along the circuit and first of all see if all the lamps are working on self check.......i think u dont have other warning lamp illuminated beside the oil lamp in normal conditions...do u?

Sierrafery - there's no bollox in your reply - you made me step back and re-look at what was going on, so thank you for your good advice and for your time in looking into all this. You are most generous.
You are quite right, what I am seeing now is the correct self check sequence and startup lights. All is now as it should be, so changing the pressure switch did actually sort it out. I was getting a bit blinkered here I think, so thank you for putting me right

oldapprentice said:

Sierrafery - there's no bollox in your reply - you made me step back and re-look at what was going on, so thank you for your good advice and for your time in looking into all this. You are most generous.
You are quite right, what I am seeing now is the correct self check sequence and startup lights. All is now as it should be, so changing the pressure switch did actually sort it out. I was getting a bit blinkered here I think, so thank you for putting me right

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i'll drink an ale on this mateop2: