I just received a very helpful reply from Ryan Linley from
https://ryanlinleyrestoration.co.uk"The middle terminal is ground as it has no insulator.
Green is more commonly used as the positive feed on italian cars (same on ferrari, alfa).
The red should be to the sensor.
It is quite often the case that the coloured washers have been mixed up during previous repairs so it may be best to test the unit with a small 9v (pp3) battery, this avoids the risk of damage during testing.
Simply connect the positive to green terminal.
negative to the central terminal.
(The pointer may show hot or cold at this point)
Now simply touch the red terminal to the center terminal for a moment.
(You should see the pointer move to the other end of the scale)
If you get no movement, repeat the process with red as pos and green as sender.
The 9v battery must be the alkaline type and not a rechargeable.
The standard alkaline battery cannot produce enough current to damage the unit👍
