[wilf leek]

Are you feeding the guage through a Voltage Stabilser? That should output around 10.5V from memory.

Even without one, the guage should read, if inaccurately.

If you short the sender wire to earth, you should get a needle deflection (probably violent, so don't hold the short for too long). If not, your guage is u/s. It is a Smiths guage after all. Sorry.
HTH