Edited: another fuel/temp gauge thread, but turns out the harness is melted together

1973 Swinger

After owning my car for 12 years, I finally have power to all of my gauges and warning lights. But the gauges aren’t functioning properly.

Presently the temperature gauge reads low even when the engine is at normal/high operating temperature.

The fuel gauge reads full when the tank is full, but reads empty when there are still 40 litres in the tank.

Where do I start to correct this problem?