Morris Minor Owners Club

OK Novice question. just noticed Yellow/Amber warning light on dash after a run into town. Flickers on tick over, getting bright as I rev. Just checked the owners handbook and says its an Oil Pressure Warning Light, There oil up to the max line on the dipstick, no mayo in the filler cap, rockers look wet with oil. And car was behaving perfectly. So piece of string length question i know but what could be going on? and is it a trip to the garage job? or a flatbed to the garage? thanks.

Ignition on, engine NOT started. Find the oil pressure switch on the side of the engine (near dizzy). Remove the wire. Does the light go out? Short the wire to earth. Does the light come on?

This will confirm that the light is wired correctly and has not been repurposed over the years by a previous owner.

Next, replace the switch. Cheap and simple DIY, it just unscrews and screw back in. Reconnect the wire.

Normal operation: Ignition on, light on, engine running, light out. May flicker slightly at very low idle,

Is all now OK? If yes, fixed, if no, then more serious issue.

Might it be the pressure differential across the oil filter? Seems more likely than the actual engine oil pressure?

oliver90owner wrote: ↑Thu Apr 10, 2025 9:23 pm Might it be the pressure differential across the oil filter? Seems more likely than the actual engine oil pressure?

Yes if this car has the blocked oil filter warning as well. Simon's suggestion of earthing the oil pressure switch wire at the engine bay end will confirm which warning lamp is illuminating on the speedo. It does sound more like the behaviour expected of the blocked filter warning.

Stephen

Thanks for your responses I''ll take a look at the weekend. And for the sake of £4.50 i've ordered a new switch. Fingers crossed

Stupid novice question but "short to earth" meaning touch bare bodywork with the wire?

Wes wrote: ↑Fri Apr 11, 2025 8:25 am Stupid novice question but "short to earth" meaning touch bare bodywork with the wire?

Bare bodywork, chassis or the engine block etc. In the case of the oil pressure switch, pull the connector off the switch in the engine block. Then take a piece of wire, poke it into the connector and touch it to the engine block. The Speedo amber light should illuminate.

Take a look at your oil filter. Is there an electrical wire coming from the top of the oil filter? If yes you have a blocked oil filter warning light, also amber but on the other side of the Speedo to the low oil pressure warning

No such thing as a stupid question, if you don't know the answer, always feel free to ask. Yes, touch the end of the wire (the female spade terminal) to any bare metal such as the engine block or parts of the body, or direct to the battery earth terminal (the one connected to the body).

The suggestion about the blocked filter warning is a good one. If fitted, this switch is on top of the oil filter head. It is not easily replaceable other than as a complete new head. You can test the circuit by shorting this wire to earth. with the ignition on the light will come on, disconnect the wire and the light will extinguish.

It is extremely rare for a blocked filter light to come on, and it indicates a lack of maintenance: oil and filter should be changed on a regular basis, no more than every 6,000 miles.

If there is no switch on the filter head, then check that there is no a loose wire touching an earth point - the wire might be unused, but still in the harness. In this case, insulate the end of the wire and secure it out of harm's way.

Great answers thank you. As for maintenance the PO was more than fastidious when it came to fluid changes so i hope i can discount that one. Will take a deeper look over the weekend.

I'll just add that 'short to earth' means bare metal, not a painted surface of any kind.
So don't just touch it to the engine block if it's got a nice paint job.

OK heres whats happened.

- Take wire off switch: yellow light stays on
- Touch wire to earth: yellow light stays on.
- Fit new pressure switch yellow light on. Start car yellow light flickers at idle and gets brighter more constant as revs rise.

Any ideas

BTW theres no sign of any wires on/near the oil filter top.

How does the red ignition light behave? Does it come on when the ignition is switched on and goes out when the engine is running? I wonder whether the two warning lights have been swapped in error and what you actually have is a fault with the charging circuit.
Good luck.

Is the wire from the warning light short circuit to earth, such as damaged insulation.
Earthing the wire puts the light on, which should not be able to happen when disconnected from the switch, as that's the earth when no oil pressure.
You could temporarily try a new wire from the warning light(earth side) to the switch

Red Ignition light works as expected/normaly

Bill_qaz wrote: ↑Mon Apr 14, 2025 7:36 pm Is the wire from the warning light short circuit to earth, such as damaged insulation.
Earthing the wire puts the light on, which should not be able to happen when disconnected from the switch, as that's the earth when no oil pressure.
You could temporarily try a new wire from the warning light(earth side) to the switch

I'll try tomorrow. to get speedo off theres a screw assessable from the glove box right? does speedo need to come off/out btw?

Question: Is the car fitted with a dynamo or an alternator?

If an alternator, and the wires are wrongly connected (at the dash), it may indicate a slip ring/brush problem or a rectifier failure.

Slip ring/brushes may be a simple change of one brush (not usually both) - or a new commutator and brushes. The alternator bearings would often be checked, too, as the front bearing can fail due to excessive belt tension (or old age!).

A failing rectifier is a replacement job.

Wes wrote: ↑Mon Apr 14, 2025 8:15 pm

Bill_qaz wrote: ↑Mon Apr 14, 2025 7:36 pm Is the wire from the warning light short circuit to earth, such as damaged insulation.
Earthing the wire puts the light on, which should not be able to happen when disconnected from the switch, as that's the earth when no oil pressure.
You could temporarily try a new wire from the warning light(earth side) to the switch

I'll try tomorrow. to get speedo off theres a screw assessable from the glove box right? does speedo need to come off/out btw?

There's a screw on either side of the Speedo accessible through a hole in the glovebox liner. Only loosen the screw by a turn, there is no need to remove it. The Speedo can then be pulled forwards and you can access the warning lights. The speedo will not come out completely with the speedo cable still attached. Care must be taken when using tools near the speedo because there are permanent live wires around there e.g to the lighting switch.

Stephen

oliver90owner wrote: ↑Mon Apr 14, 2025 8:38 pm Question: Is the car fitted with a dynamo or an alternator?

If an alternator, and the wires are wrongly connected (at the dash), it may indicate a slip ring/brush problem or a rectifier failure.

Slip ring/brushes may be a simple change of one brush (not usually both) - or a new commutator and brushes. The alternator bearings would often be checked, too, as the front bearing can fail due to excessive belt tension (or old age!).

A failing rectifier is a replacement job.

alternator -Earth

But this has only just happened and ive driven maybe 2-300 miles since buying the car

svenedin wrote: ↑Mon Apr 14, 2025 8:57 pm

Wes wrote: ↑Mon Apr 14, 2025 8:15 pm

Bill_qaz wrote: ↑Mon Apr 14, 2025 7:36 pm Is the wire from the warning light short circuit to earth, such as damaged insulation.
Earthing the wire puts the light on, which should not be able to happen when disconnected from the switch, as that's the earth when no oil pressure.
You could temporarily try a new wire from the warning light(earth side) to the switch

I'll try tomorrow. to get speedo off theres a screw assessable from the glove box right? does speedo need to come off/out btw?

There's a screw on either side of the Speedo accessible through a hole in the glovebox liner. Only loosen the screw by a turn, there is no need to remove it. The Speedo can then be pulled forwards and you can access the warning lights. The speedo will not come out completely with the speedo cable still attached. Care must be taken when using tools near the speedo because there are permanent live wires around there e.g to the lighting switch.

Stephen

Top tips. thanks