Reply to "Some good...some bad! It passed the MoT test ... But it over heated on the way home."

Pish, there is one sender but two possible Veglia gauges. '71-72= 0-220F; '73-up= 0-260F. The 260 gauge is far more valuable due to its extended range and (I think) has better stock calibration. Whichever gauge/sender you use, the assembly should be calibrated to your car for better accuracy. You do this with engine running and a trusted glass thermometer in the header tank and a handful of small resistors to temporarily patch into the line from sender to gauge. Write down the two sets of temps you'll get- the variance will be greater at one end or the other of the range. If you want the last bit of accuracy, a variable resistor can be used. Then you solder in a resistor giving the closest value to true. The two gauges are not interchangeable once you calibrate the system.

Not to load you up with possibilities, but with a stabilized temperature after driving a bit, turn on the headlights. If the gauge temp drops instantly & noticeably, there is a grounding problem somewhere in your 44 year old system. All the small-gauge grounding wires are 'daisy-chained' one to another so it will not necessarily be the water temp gauge ground wire.