Oil Warning Light Troubles

[KevinB]

Hi everyone, my first post here. Some advice please.

I bought a 1967 1098 saloon last year and the oil pressure warning light has never worked, though a mechanic has checked the car and assures me the pressure is fine. But I want the light to work. So I've first been checking the bulbs behind the speedo.

There are two bulb holders that are loose. Please see photo below.

1. The Green/Yellow wired one is I believe the oil light and it has power but no earth, with the ignition ON. And if I put in a bulb with the engine not running, it does NOT light.

2. The Green/Brown one is powered and earthed all the time, irrespective of if the ignition is ON or OFF. If put in a bulb, it lights. What is this holder for? I can't find it on the wiring diagram in the Haynes manual.

Please suggest what I should do to make the oil light work. Thanks in advance.

Kevin

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[geoberni]

Green/Brown doesn't make sense, it was only officially used for one cable, and that was only on cars with the DB10 Indicator system pre 1963...

What have you got at the engine?

What colours are on the Oil Pressure Switch? (by the Distributor)
What colours are on the Oil Filter Blockage Switch (on top of the oil filter housing)

Both of these should be the same colours (Green/yellow).

You'll need to get a multimeter and continuity check them both through to the lamp holders.

[KevinB]

Thank you for the reply. So the Green/Brown is a puzzle? And worrying it's powered all the time.

I have Green/Yellow at the pressure switch and it has power, so I suspect there is continuity to the wire at the warning light. But the distance is too much for my meter.

I cannot find any wires at the filter.

Kevin

[svenedin]

Oil pressure switch in my car has a green/brown wire going to it. I can only say that from my library of photographs because my car is away at the moment. With the engine stopped and the ignition on, the circuit should be complete and the oil pressure warning light is lit. With the engine running the oil pressure should cause the switch to open and the light goes out.

Green/yellow is the oil filter blocked warning. This is normally off. A blockage causes the switch to close and the circuit is then complete and the light comes on.

So the two warning lights work differently. One circuit is closed with the engine off; the other is open.

You simply have the wrong wire going to the oil pressure warning switch

Stephen

[KevinB]

Thank you.

I've checked for continuity from the terminal on the oil pressure switch to the engine block with the engine stopped and there's none. So circuit incomplete?

So maybe my oil pressure switch is faulty

[KevinB]

Sorry Stephen, just seen your suggestion it may have the wrong wire at the oil pressure switch. I will investigate ...

Kevin

[geoberni]

Thank you for the reply. So the Green/Brown is a puzzle? And worrying it's powered all the time.

I have Green/Yellow at the pressure switch and it has power, so I suspect there is continuity to the wire at the warning light. But the distance is too much for my meter.

I cannot find any wires at the filter.

Kevin

I just realised I wasn't totally correct on my previous statement about Green/Brown, though it is still very much a puzzle.
It was still used on post '63 cars, but again only in one place, connecting the Flasher Unit to the Indicator Switch, nowhere near a lamp holder behind the Speedo.

There have been occasional cases of wiring not following the colours in the manual, I think sometimes they must've run short of a particular cable so used a differently marked one in places it wouldn't be seen...

You can extend a Meter cable with any old length of cable and some insulation tape.

The Oil Filter with the Filter Blockage switch looks like this :
https://www.sportsandclassics.com/wp-co ... 12x384.jpg

If you have a Spin on oil filter conversion, then the original housing and switch has been removed, so there'll be some tided back, or even cut off, wiring somewhere nearby (ish) depending on the person who did it....

You've said:

1. The Green/Yellow wired one is I believe the oil light and it has power but no earth, with the ignition ON. And if I put in a bulb with the engine not running, it does NOT light.

If the engine is not running but the Ign Sw is on, then the Oil Lamp should light , so this isn't the Oil Light.

2. The Green/Brown one is powered and earthed all the time, irrespective of if the ignition is ON or OFF. If put in a bulb, it lights. What is this holder for? I can't find it on the wiring diagram in the Haynes manual.

What's puzzling here, apart from the colours used, is how this is powered with the Ign Off ???

[geoberni]

Oil pressure switch in my car has a green/brown wire going to it. I can only say that from my library of photographs because my car is away at the moment.

So they did deviate from the standard colours....

What colour do you have coming from Flasher Unit to the Indicator Selector?

[simmitc]

With the ignition ON, power is supplied to the oil pressure warning light. From there, it travels down the wire to the OPWL switch. 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.

When fitting a new switch, do not use PTFE tape or similar, you need a good contact with the block. The switch is a simple screw thread.

[svenedin]

Oil pressure switch in my car has a green/brown wire going to it. I can only say that from my library of photographs because my car is away at the moment.

So they did deviate from the standard colours....

What colour do you have coming from Flasher Unit to the Indicator Selector?

Yes. See photo. I'll look for a picture of flasher unit shortly. Answer: another green/brown

Stephen

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[KevinB]

Thank you all. I'm going to need to work through all the suggestions carefully tomorrow.

It's definitely a green/yellow wire to the oil pressure switch on my car and the wire looks like it’s been there for many years.

It does NOT have a spin-on filter conversion, but l can see no evidence of a filter blockage connection ever being there. The photo of that above does not display at myend unfortunately.

I have ordered a new oil pressure switch.

Kevin

[geoberni]

Yes. See photo. I'll look for a picture of flasher unit shortly. Answer: another green/brown

Stephen

So my theory of them using whatever was to hand, at least in certain circumstances, seems to ring true....

Basil's Oil Pressure Switch is Green/Yellow, as per the manual, but then he's got a new loom circa 1990s, so not Morris original

Your loom in “Xavier” looks new though....

[svenedin]

Yes. See photo. I'll look for a picture of flasher unit shortly. Answer: another green/brown

Stephen

So my theory of them using whatever was to hand, at least in certain circumstances, seems to ring true....

Actually the oil pressure switch photo is the original loom. The flasher unit photo is a new loom. I do still have the old loom so I could find the flasher connections. Old loom is filthy though. Another day!

Stephen

Basil's Oil Pressure Switch is Green/Yellow, as per the manual, but then he's got a new loom circa 1990s, so not Morris original

Your loom in “Xavier” looks new though....

[svenedin]

Whoops. That’s messed it up. Typing on a phone…

Stephen

[geoberni]

Whoops. That’s messed it up. Typing on a phone…

Stephen

OK, I think I've got that....

Actually the oil pressure switch photo is the original loom. The flasher unit photo is a new loom. I do still have the old loom so I could find the flasher connections. Old loom is filthy though. Another day!

Stephen

So the Flasher unit is new and as per the Wiring Diagrams whilst the Oil Switch is incorrect according to diagrams, but original factory fit.

[Bill_qaz]

My 62 is green and brown at the switch, original wiring

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[svenedin]

Whoops. That’s messed it up. Typing on a phone…

Stephen

OK, I think I've got that....

Actually the oil pressure switch photo is the original loom. The flasher unit photo is a new loom. I do still have the old loom so I could find the flasher connections. Old loom is filthy though. Another day!

Stephen

So the Flasher unit is new and as per the Wiring Diagrams whilst the Oil Switch is incorrect according to diagrams, but original factory fit.

Yes. I have now found another old photo. With the old original 1969 loom, green/brown to oil pressure switch and green/brown to flasher unit. With new loom exactly the same. Green/yellow to blocked oil filter warning

To the speedo low oil pressure warning light there is a green wire and a green/brown wire

Stephen

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[geoberni]

So Bill has also got Green/Brown to the Oil Pressure Sw on his '62...

Yet the Manual wiring diagrams, right back to the earliest Centre Speedo one, shows Green/Yellow. I wonder when the loom makers went rogue

I've done some internet research and the Lucas/British Standard chart only a Lt Green/Brown for the Flasher circuit.
Green/Brown, only appears later when it was used for Switch to Reversing Lamp.

I think it's time to say the wiring for the Oil Pressure light is whatever your particular car has....

[mobylette]

My 1961 has green/yellow, original loom.

[Bill_qaz]

My 1961 has green/yellow, original loom.

So possibly the change is mk5 <1962 ?