If the car is fitted with Smiths instruments, there is often an
electromechanical 'regulator' on the back of the instrument cluster. This
has a bi-metal switch with a resistance wire wrapped around it inside the
little box it lives in. If it runs the same voltage as my Land Crabs used
to have it averages out at about 7.5 volts to the temperature gauge
circuit..... in 12 volt on / off pulses! I didn't have many of these units
fail during the 25 years / 450,000 MILES I did in my Austin 1800's, but
when they do fail, the temperature gauge and fuel gauge stop working!

Perhaps you have a wire that has dropped off or broken, or alternatively a
fuse or connector on the fuse box that is faulty.

The instruments in these BMC beasties were run from the ingition circuit
via their own contact on the back of the ignition switch, (for the cars
without the "Acc" position on the switch this is common with the Ign
terminal)

Pip

Hi

It wasn't broke, just resting.  Thought i would try and give the instrument
cluster a tap before i got the screwdriver out and hey presto-cured.

Must have a bad connection somewhere in there, at least i know which end the
fault is if it happens again.

thanks for all replies

Gary