MK V Fuel Sender

Hello All.

I am testing to see if my entire fuel gauge and sender unit is all working OK.
I am starting with my fuel sender.

Those with previous experience may be able to help identify if all internal parts seem to be in order.
Is there a series of tests I can perform with a simple multi-meter or anything in particular I could be checking?
The OHM reading starts at about 5ohms on an empty tank and then rises to around 70ohms at around 3 quarters full but after that they jump around quite erratically into the hundered.

Any advice would be greatly appreciated.
Thanks Frank

Hi Frank,

I’m having trouble with my MKV fuel gauge. I found that the float arm was seized so it was freed with some WD40 and some gentle persuasion. A multi meter to check resistance will tell you if it’s working correctly. It looks pretty clean and undamaged to my eyes.Then I guess it’s a matter of testing the wiring to make sure that the two wires carry current to the fuel gauge. Polarity matters for the wiring so check with the Service Manual. I think that if you have the wrong polarity the gauge will read like this on my car with the low fuel warning lamp on.

I need to pull my gauge out and have it serviced as it’s a bit sticky at present.

Hope this helps?


Hi Frank,
You can put an ohm meter with one wire grounded on the body and try the other one on each terminal, one will measure resistance as the float moves, and the other should only make a contact when the float is in the empty position. The resistance is not critical but should generally increase with movement in one direction.

Thanks so much for your replies gents. It is greatly appreciated.

I have tested the sender unit and I think this is OK. Ohm meter reading ranges from about 5 (empty) to around 70 (full) and rises/dips evenly when float arm is moved at a constant rate either way. Both wires from gauge to send unit seem fine as well.

As mentioned by Rob, when checked for continuity between both wire terminals on the sender, I was only able to achieve continuity when the float level was close to empty. I assume this sends a return signal back to the gauge to activate the low petrol lamp?

Now I shall turn my attention to the gauge, which has not shown any signs of life in the slightest, even when ignition is on or wires are attached or taken off. It is happy sitting on empty. I have tried the workshop manual suggestion to supply the gauge with power and disconnect the tank sender wire. It makes no difference and stays on the Empty position.

I have removed the gauge completely from the car. If I hold it in its normal position and facing me, it reads empty and if I turn it upside down and facing me, it reads full. The transition between both when I am turning it is smooth.

On the rear of the gauge it has a B connection terminal (power), a T connection terminal (to tank sender) and a 3rd unmarked terminal connection. This third unmarked terminal supports the return wire from the tank sender which makes contact with the low petrol lamp.

Is anyone able to confirm the where the Earth contact point is for the gauge and if the fuel tank or tank sender unit needs earthing?

19 green/yellow on the center terminal with a tab over to the tip of the bulb gets grounded in the sender when the level is low and turns on the bulb.
17 green connected to terminal B is the 12v negative supply from the voltage regulator, and there is a blue conductor over to the side of the bulb.
24 green/black is connected to terminal T and goes through the resistance to ground in the sender, which moves the needle.
The other two nuts in the slots hold magnets which adjust the movement of the needle if it sticks.

There is some excellent information on the MGA website regarding this type of gauge.

Hi Frank,

I have to take my gauge to have it serviced / checked over. I’m in Melbourne too. I would use Howard Instruments but they have a turn around time of over four months at present. Ringwood Speedometer Service, 693 Whitehorse Road, Mitcham was recommended. I also found these people at Cheltenham, if they are closer to you?


Thanks so much for your detailed response Rob.
I have now solved the issue. I simply forgot to earth the gauge once I had removed it from the dash. I have now got everything working in perfect harmony, although as a temporary set up with the fuel sender attached to the gauge on the front seat. All works well. Hopefully I will find the same when I put everything back in their right places.

Thanks Tim. Have it working well now. Just forgot to earth the gauge after I removed it from the dash. Thanks for the repairer suggestions. I knew of Howard’s but not auto marine instruments. They may come very handy in future as I am located in Cheltenham and the petrol gauge was the first gauge I have tackled during my restoration. Plenty more to check out in time through!!!