Morris Minor Owners Club

When was the blocked oil filter warning introduced? It would make sense to me that the wire colour to the oil pressure warning light was changed when the blocked filter warning was introduced. Changing the wire colour avoids confusion with two wires that are both green/yellow in a similar place (they could be misconnected). This is despite the fact that some cars have the wiring for the blocked filter warning but they don't have the filter head that incorporates the warning switch......

Stephen

svenedin wrote: ↑Tue Feb 17, 2026 10:24 am When was the blocked oil filter warning introduced? It would make sense to me that the wire colour to the oil pressure warning light was changed when the blocked filter warning was introduced. Changing the wire colour avoids confusion with two wires that are both green/yellow in a similar place (they could be misconnected). This is despite the fact that some cars have the wiring for the blocked filter warning but they don't have the filter head that incorporates the warning switch......
.


Stephen

According to your friends ESM minor history on their site:
https://www.thedeebees.com/a-minor-history/

1964 the interior received its final update, with a new heater unit (now with fresh air ventilation), and from October of that year, a modified dashboard with toggle switches, white-on-black speedometer unit (incorporating a warning light for a blocked oil filter),


Mine doesn't have the filter blocked light in speedo

simmitc wrote: ↑Mon Feb 16, 2026 4:24 pm If you have 12 volts at the switch then the circuit and bulb are OK. Remove the wire from the switch and short it directly to earth. The lamp should illuminate. This will confirm that all is OK, but the switch needs replacing - a simple task.

You have already shown that there is no continuity in the switch to earth, so that shoiws that the switch is faulty, the above is to prove that it is the only problem.

SUCCESS!
As simmitc suggested (thank you), I shorted the green/yellow by the oil pressure switch to Earth and the lamp at the speedo lit up! So the wiring is OK and it needs a new switch, which I have ordered.

Also, I found a green/brown by the engine, connected to the starter solenoid. See photo. This MAY explain why the bulb holder by the speedo is permanently powered?

Sorry the photo is sideways.

The green/brown wire with that characteristic insulation sleeve IS the wire that goes to the oil pressure switch. It should absolutely not be connected to the starter solenoid! The green/yellow wire is for the blocked oil pressure warning which you do not have so it is redundant.

Remove the green/brown wire from the solenoid and short it to earth. Does the speedo lamp light up when shorted to earth and go out when not shorted?

You cannot use the green/yellow wire for the oil pressure switch or you will end up with a warning bulb that works backwards to normal; on all the time and goes out when the oil pressure is too low!

Stephen

svenedin wrote: ↑Tue Feb 17, 2026 11:47 am The green/brown wire with that characteristic insulation sleeve IS the wire that goes to the oil pressure switch. It should absolutely not be connected to the starter solenoid! The green/yellow wire is for the blocked oil pressure warning which you do not have so it is redundant.

Remove the green/brown wire from the solenoid and short it to earth. Does the speedo lamp light up when shorted to earth and go out when not shorted?

You cannot use the green/yellow wire for the oil pressure switch or you will end up with a warning bulb that works backwards to normal; on all the time and goes out when the oil pressure is too low!

Stephen

Thanks, but I'm thoroughly confused now! The wiring diagram I have in the Haynes manual clearly shows the green/yellow going to the oil pressure switch.

But, I don't like having a permanently powered holder behind the speedo, if it's not used. So removing the green/brown from the solenoid seems a very good idea.

Could someone please post a photo of an oil filter warning switch? I'm just not sure what I am looking for there.

Kevin

I didn't see any discussion about the green with brown bulb socket being powered all the time. Take a look at the fuse box and see if there is a green wire on a different terminal than the other green wires. If so check to see if it goes to the socket in question. Once this socket is also powered with the ignition switch, you can use either socket for the oil pressure.

The green/brown bulb holder was powered all the time by accident because it was connected to the solenoid in the OPs car!!

Yes this is confusing I admit. The wiring diagram in the workshop manual, appropriate for the later car, shows green/yellow wires being used for BOTH the oil pressure warning light and the blocked oil filter warning light. In the discussion above, we have established that this is not correct and that in some cars, the correct wire for the oil pressure switch is green/brown. To add to this confusion, the wire is provided for the blocked filter warning but in some cars the filter head does not have a blocked warning facility.......

Does that make some kind of sense now?

Stephen

My engine coming out for refurbishment. Filter electrical connection arrowed

I see know that it's connected to the battery feed to the solenoid. When the ignition is on, there is a power loop. This is an example of someone "fixing" an electrical issue, but actually causing other troubles, which is what gave Lucas a bad name is some circles.

svenedin wrote: ↑Tue Feb 17, 2026 12:53 pm The green/brown bulb holder was powered all the time by accident because it was connected to the solenoid in the OPs car!!

Yes this is confusing I admit. The wiring diagram in the workshop manual, appropriate for the later car, shows green/yellow wires being used for BOTH the oil pressure warning light and the blocked oil filter warning light. In the discussion above, we have established that this is not correct and that in some cars, the correct wire for the oil pressure switch is green/brown. To add to this confusion, the wire is provided for the blocked filter warning but in some cars the filter head does not have a blocked warning facility.......

I have now removed the green/brown wire from the solenoid!! I can't imagine why that was ever put there. Thank you for pointing it out - it was a safety hazard, I think.

Now, both the green/yellow and green/brown wires function in an identical way. If either wire in the engine bay is shorted to earth, the relevant lamp at the speedo lights up.

So my conclusion is that it doesn't really matter which wire I use for the oil pressure switch (if it's long enough). Or indeed a filter switch (if I had one) - thank you for the photo.

Please correct me if you don't agree.

My plan now is to wait for the new oil pressure switch and fit it. Hopefully, that will make a light come on and off, as expected.

Thank you all for the help.

Kevin

I have now fitted the new pressure switch, using the green/yellow wire and the dashboard light is behaving as expected. It lights when the ignition is turned on and goes out once the engine is running.

Thank you all for the help.