408 Fuel gauge not working diagnosis - opinions, pls?

[Roger Morrall]

0 to 60 ohms sounds about right, but I’m sure you’ll check it actually drives the gauge correctly before you put it back. I say this as I’m slightly surprised that your gauge was showing empty with a duff sender - my experience was that the gauge showed well over full when the sender was duff and open circuit.

There is a relatively simple explanation of how these gauges work at Fuel Gauge - Working or not?

I know this describes a pre war Austin seven but the principle didn’t change over the years and it’s quite a good description.

Note that the body of the gauge itself has to be earthed, also that because this type of gauge relies on two opposing electromagnets it’s accuracy is relatively unaffected by battery voltage and it doesn’t need a voltage stabiliser - so don’t go looking for one as there you’ll never find it, there ain’t one. This type of gauge gives you an instant indication of the level in the tank when you switch the ignition on unlike the bimetallic gauge which was used on many other cars of the period which takes a little time to show what’s what and does need a voltage regulator. On the other hand the electromagnetic gauge does rather wobble about as the fuel sloshes in the tank which the bimetallic gauge doesn’t.

You won’t find it at all easy to find an original sender if you do need one but these guys

https://www.smiths-instruments.co.uk/


will be able to supply a modern substitute - you will need to quote all the letters and numbers on the original - if you go to their web pages Products then Senders you’ll understand why - the variety available is totally bewildering

Good luck