1973 Duster - Fuel and Temp Gauge issue

Hi
We're trying to revive a 73 Duster 318 that's been off the road for many years.
It's running now but we have a problem with the fuel and temp gauges. With the ignition on, and engine off the temp gauge is on bottom stop and the fuel gauge shows fuel in the tank. When the car is started both gauges go right over to the stop.
We've tried another Voltage Limiter and put an additional earth wire from the cluster but no joy. The ammeter shows a quite high level of charge too - could it be a Voltage Regulator problem and it's overcharging?
Thanks, Harvey