Temp Gauge Issues

Hey Guys,
I’ve got a 72 Demon with non rallye dash, temp gauge has never worked, all other gauges working including fuel.
Have replaced sending unit and tests cable going to it and it is all good.
So I narrowed it down to a faulty gauge, pulled the gauge and replaced it with a new one and it’s still not working, also now my fuel gauge is playing up which it wasn’t before. Do you guys think it’s an issue with the voltage regulator or the circuit board itself?
Thanks in advance for your help
Cheers from Oz
Mike
When I had problems with my 72 demon, non rally dash, it was the regulator on the dash. Mine read to hot. I would get a factory service manual. You could also have a wiring problem at the bulk head.