Cork is a natural product you can buy from an auto parts store but you need a hole punch
Blue tack is a good alternative. Well done

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1960 Morris Mini Minor

I agree with Phillb. It sounds like the voltage regulator.
It has its own bimetal strip that switches on and off to give an average of about 10 volts. (It is difficult to measure with a digital voltmeter as it changes every second or so). This is to ensure that the varying generator speed and hence output voltage doesn't make the gauges swing up and down (your apparent problem). As Phillb suggested, look at the fuel gauge. Does it also creep up and down with the generator speed (depending on the bimetal strip wiring it might actually fluctuate in the opposite direction)?
It is easier to replace the voltage regulator with an electronic one than risk stuffing up the gauge.

I've got the same problem and it was fine for a number of year but lately when you get out on the open road the temp drops down to almost the C on the gauge but reads normal while driving around town.
I asked about this at the 60th anniversary of the Mini in Melbourne.
It was suggested that the cork may be missing or could have fallen out of the adjustment hole's on the gauge.
I haven't got around to fixing this issue yet
If the cork is still in place in the adjustment hole's on the gauge then would it defiantly be the voltage stabilizer or the earth?

Well I finally plugged the holes with blu tack and went for a drive but still waaay too sensitive dropping to C and rising to 3/4.

Interesting about the fuel gauge and the voltage regulator for the instruments. The fuel gauge needle is also quite sensitive. I’ve got some super steep hills so I’m going to test how quickly the fuel gauge needle moves.


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Australian 69 DeLuxe w/ hydro suspension. Single HS4 (twin HS2 being assembled). 1275 1100s engine (998 due for rebuild) . Clubman remote gear change. Automatic front subframe.

Wait a minute... are you saying the instrument voltage regulator is only used when you’re using a generator? I’m on an alternator, negative earth.


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Australian 69 DeLuxe w/ hydro suspension. Single HS4 (twin HS2 being assembled). 1275 1100s engine (998 due for rebuild) . Clubman remote gear change. Automatic front subframe.

Maybe we should be calling the one behind the speedo a voltage stabilizer. An alternator or generator both have a voltage regulator.

Might start experimenting with an earth. Will run a 4mm cable from the back of the voltage regulator to good earth somewhere.

Unless I’m not supposed to be using a voltage regulator with an alternator!!???


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Australian 69 DeLuxe w/ hydro suspension. Single HS4 (twin HS2 being assembled). 1275 1100s engine (998 due for rebuild) . Clubman remote gear change. Automatic front subframe.

You can test if the voltage stabilizer is stuffed or if its doing something at least with a digital multimeter. It wont be accurate if the stabilizer is working. It will read on and off. You will have flutuations like 5v 12v 0v 10v 5v 10v 0v 12v. If the bimetalic strip or windings inside the stabilizer is stuffed it will give you 12v constant.

Check you are getting 12v at the B terminal then check what is going on at the I terminal

Oohhhh. I see. Of course. The generator has a that voltage regulator. I’m not running a generator.... neg earth alternator. For a second I thought “what the hell...”

Yes. The voltage stabiliser (small metal box with about 4 spade terminals) usually found on the back of the speedo gauge.... that is my next troubleshooting experiment.

So who knows how to test one of these things? Like I mentioned in my prev post, I’ll run a new earth lead somewhere else first.

Been trying to find a click in the driveshaft all week... but that’s another topic


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Australian 69 DeLuxe w/ hydro suspension. Single HS4 (twin HS2 being assembled). 1275 1100s engine (998 due for rebuild) . Clubman remote gear change. Automatic front subframe.

Legend. Tomorrow’s job!!!


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Australian 69 DeLuxe w/ hydro suspension. Single HS4 (twin HS2 being assembled). 1275 1100s engine (998 due for rebuild) . Clubman remote gear change. Automatic front subframe.

Just earth the neg lead of the multumeter to a good known earth and test the B and I with the pos lead. When i gave 12v as a reference it will actually be system voltage of 13.5v or 14v

It may also work for a few minutes then go to system voltage when it gets hot. Give it a bit of time or test it when hot.

Here is a schematic of what is going on inside.

Sorry. I called the instrument voltage stabilizer a voltage regulator by mistake. The black plastic box on the driver's side of the engine bay is called a Control Box by Lucas but many people call it a voltage regulator.
Alternator cars have less voltage fluctuations than generator cars but still need the instrument voltage stabilizer as the voltage does drop at idle.
I found a spare 7810 electronic (also called a voltage regulator) component that you can build inside the original metal stabilizer box if you want it. Dave D

Is there a way of testing these out of the car?

You should be able to bench test it with a 12v power supply. I sometimes use a battery charger for small jobs like this.

Pos to the B and Neg to the body. Then use a voltmeter between the I and body. A digital multimeter is not the best to use but will tell you if the contacts are opening and closing or staying closed.

Because there is an internal load (the windings) inside the stabilizer there shouldn't be the need for another load placed between the power leads.

Finally put a multimeter on the voltage stabiliser on the back of the speedo today. The voltage jumps around like you say. Forgot to check the B terminal though.


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Australian 69 DeLuxe w/ hydro suspension. Single HS4 (twin HS2 being assembled). 1275 1100s engine (998 due for rebuild) . Clubman remote gear change. Automatic front subframe.