It's a roundy with aftermarket temp gauge And recently installed one of wombats electronic stabilisers, haven't checked voltages in and out but will have a look on the weekend.

Just to clarify my previous comment about never to feed 12 Volt positive to fuel sender.

The fuel and temp gauges on a Mini are very simple. They both work the same way. Ignition 12 Volts is fed to the Voltage Stabilizer (some people call it Regulator). This unit drops the 12 Volts down to 10 Volts and supplies the gauges. The gauges have two terminals each, with 10 volts going in to one terminal (does not matter which one). The second terminal is connected to the fuel or temp sender units.

The sender units both work in a similar manner. Temperature sender varies the resistance with heat and the Fuel sender by means of the float on an arm which moves up and down according to the level of fuel in the tank. These senders have a resistance which varies. The gauge gets it's negative connection to earth through the resistor and the needle reads accordingly. Usually the lower the resistance the higher the gauge reads. Therefore if you ground the sender wire the gauge will go right up to HOT or FULL. Gauge that reads full when ignition is turned on could mean there is a sender wire grounded somewhere in between the two points. Gauge that reads COLD or EMPTY can mean that sender has no contact to earth or sender is open-circuit.

Many times I have found the following problem with fuel gauges reading full all the time, especially on Minis that have been "restored". As the rear wiring loom on a Mini goes up the left windscreen pillar and along the inner roof channel I have found screws used which were too long in both interior lamp (two screws) and rear side window latch (two screws) that have been screwed through the wiring. Sometimes they hit a lights wire and cause a short or sometimes the fuel gauge wire. On the other hand if the fuel reads empty all the time I would be checking the sender unit to see if it has got an open circuit resistor or perhaps the float itself has developed a crack or hole and filled up with fuel, so will no longer float like it should.

Never attempt to feed a full 12 Volt to a sender unit as the sender unit resistor will get hot and fuse which will ignite the fuel in the tank.

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DID I MENTION THAT I AM THE BEST SUPPLIER FOR MINI ELECTRICAL PARTS AND REPAIRS?
"Let us remove your "SHORTS"

Great summary Tony. The forum members thank you for the expert explanation.

P.S. I made some minor changes to your post such as spacing into several paragraphs for improved readability and hence understanding.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

I am currently rewiring my deluxe. Great explanation Tony, helps heaps.

Something else to consider
If the gauge reads full Or higher than it should.
Possibly the Reg is not regulating the voltage at 10 volts.

Poor earth leads to firstly variation in output then eventually burn out of Stabilisers which eventually leads to variation (positive or higher reading) then burn out ( full scale deflection ) of gauge.
Both essentially become a pass through device rather than regulated devices.
Bear in mind that the gauge can stretch and read higher even after you replace the stabiliser.
Take care with grounding the wire to check deflection. It tells you little other than the fact that there is continuity. Use a variable resistance. If you have a spare fuel sender earth the body of the sender and use it as your test device. You dont need a fancy tool for this. You do however need the correct tool to measure the output voltage accurately of bimetallic Stabilisers. A multimeter wont do it. A test light will only show the opening and closing of the points inside the stabilizer as will a power supply if the whole system is set up.
What do i mean by burn out?. The gauge and original stabilisers have a wire wound bimetallic strip.
The wire is a fixed length and resistance value. V=IR old man.
The wire winding is insulated in cloth so it does not touch the strip itself but heats two dissimilar strips of metal bonded together back to back in the strip which causes deflection in the pointer or deflection in the gap/ timing of the opening and closing of the points in the stabiliser
This is why the cork plugs in the back of both gauges are important. They cover the adjustment slots . If they are left uncovered the cold air gushes in as you drive and the gauges read less.
There are small holes in the side of the gauge to allow a little warm air out so the glass does not fog.
Dont fill them with paint etc.

A note to gto a regulated system means that a variation in the input voltage In the system does not affect the output of the stabilizer. They are quite resiliant bimetal regs providing the earth to them is good.
If you buy an electronic stabilizer ideally it should drop to 0 volts if it Looses earth to save it and the gauges. I say ideally as most don't.
Finally test your earths Everywhere...Some look at it from the perspective of resistance with respect to the negative terminal of the battery. Others consider voltage drop. This is a whole other topic.

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1960 Morris Mini Minor

If any one has any burnt out Voltage stabilizers please don't throw them out but please send them to me for modifying into Electronic. I can't do any without the old cases. Cheers.

_________________
DID I MENTION THAT I AM THE BEST SUPPLIER FOR MINI ELECTRICAL PARTS AND REPAIRS?
"Let us remove your "SHORTS"