Please post a picture of the "back" side of your fuel gauge.  The picture needs to show as much of the back as possible without the wires obstructing too much of the view.  Please pull them aside or shoot your picture from a couple of different angles.

Disconnect the wires from the sending unit, connect a multimeter across the sending unit terminals, and use a coat hanger through the tank filler neck to lift the sender float all the way to the top, then push it down to the bottom.  Let us know the resistance readings you measure at the empty/full extremes.

A few of your comments concern me.  Your message implies that the car came to you disassembled and that the car did not have a voltage stabilizer.  Did the fuel gauge ever work properly for you since you owned the car?  When you mounted the Lotus voltage stabilizer... how and where did you mount it?  Was there a mounting bracket for a stabilizer on the back of the Mini speedometer?

You may want to take your VIN number and look it up to confirm the year of build vs the year of registration.  Gauges whose needles "snap" to position when the key is turned to the run position are the earlier type.  A car that is registered as a '65 could in reality be a '64.  

dklawson, thanks for your note.
What year is your Mini?
    1965 Austin Cooper S.  Mostly stock, I think.
Pre-1965 uses magnetic gauges where the needles "snap" to position when the key is turned to the run position.  
     My gauge "snaps" to full.
The early cars with the magnetic gauges have a different sender than later cars.  If the green/black wire is removed (knocked off) of their sending units or if the black earth wire is removed/broken the gauge will "jump" to full.  Check that the both the black and green/black wires are on the sending unit.
    Black and green wires are solid on the sending unit.
If your car was made in 1965 or later, a short between the green/black wire and ground will make the gauge read high/full.  
    I will have to check this out.
As for the voltage stabilizer, that showed up in 1965 (late '64).  If the stabilizer is not working one of two things happens.  A totally burned out stabilizer will not pass any voltage and the fuel gauge reads below empty.  If the stabilizer loses its ground connection (either internally or via its mounting tab) the stabilizer will pass the charging system voltage (close to 14V).  When that happens the gauges read as much as 40% high. 
    I actually installed a spare voltage stabilizer I have from my Lotus.  The Mini did not have one in the many boxes of parts       that came with the Mini.  The wiring diagram shows a voltage stabilizer so I installed the spare I had.  I will have to check if it is working.
Let us know if it bolts onto the tank or is secured with the bayonet locking ring. 
    My sending unit is mounted with the bayonet or cam locking ring.  I did a check on the sending unit when I was rebuilding the Mini and it did check out, at least I had a variable resistance out of the unit.  Had no idea as to what the readings equate to.

I need to do a little more checking on the complete gas gauge system.

Thanks all for the help.
Regards
Tim

Lol...yes Dan
I was going to "rag" on Don also about spelling "Thru"...but thought better.

I'm actually happy this thread came up as My gauge is reading below empty , aka: not working.

Doug left a very informative post there.  My car is a 62, but with some later than 64 bits added....gauge may be one of them

By the way, if voltage stabilizers are a bit of a mystery, I'd suggest reading //www.minimania.com/Smiths_Voltage_Stabilizers , written by our own DK.

 

Wow, tough crowd!  I mis-typed ...

I installed the 7.5 UK gallon tank (34 liter).  I was using the 5.5 UK gallon (25 liter) tank, now I'm just storing it as a collectible.

would that rule of thumb year wise apply to Mokes?

Hey Spitz. You should know that! Weren't you the guy ragging me a while back about spelling "gray"/"grey" properly?

Ah....right  ( but that's Imperial, not UK )

But 39 litres is 10 little US gallons

7.5 UK Gal. 9 US Gal.

39 litre tank?  Thats a little more than 8.5 gallons, I thought the larger(later) MINI tanks were 7.5 Gallon….what tank do you have jeg?

Thanks Chuck - I replaced my sending unit a couple of years ago when I installed the big 39 liter tank and it's always read a bit high.  I've got a new voltage stabilizer sitting in the storage box o'electrical bits, so I'll give it a whirl.  

lucky you. 



(sender unit)

What year is your Mini?  Pre-1965 uses magnetic gauges where the needles "snap" to position when the key is turned to the run position.  1965 and later cars use the bimetallic gauges whose needles slowly climb to their reading when the key is turned to the run position.

The early cars with the magnetic gauges have a different sender than later cars.  If the green/black wire is removed (knocked off) of their sending units or if the black earth wire is removed/broken the gauge will "jump" to full.  Check that the both the black and green/black wires are on the sending unit.  Let us know what you find and what year your car is.

If your car was made in 1965 or later, a short between the green/black wire and ground will make the gauge read high/full.  

As for the voltage stabilizer, that showed up in 1965 (late '64).  If the stabilizer is not working one of two things happens.  A totally burned out stabilizer will not pass any voltage and the fuel gauge reads below empty.  If the stabilizer loses its ground connection (either internally or via its mounting tab) the stabilizer will pass the charging system voltage (close to 14V).  When that happens the gauges read as much as 40% high. 

Again, post back with the year of your car and take a look at the fuel sending unit.  Let us know if it bolts onto the tank or is secured with the bayonet locking ring.

Fuel and temperature gauges reading way too high = bimetalic voltage stabilizer kaput.

Hello.
Man when it rains it pours.  So I stopped at the shop and tried to view the fan and other stuff.  Started Yoda up and noticed the gas gauge is full.  Well that can't be.  I just drove it 200 miles since the last fill weeks ago.  I record this info because that's what I do.  I know, anal, somewhat.
Anyway, turn key off, needle goes to E.  Turn key on, needle moves fast or jumps to full.  What the heck!!

Is there a straight forward way to test the float?  I would guess there should be a voltage out or something our of the float.  Also how to test the gauge?  Electrical power of ?? is equal to half full.  Electrical power of ?? is full?

Thanks much
Tim