Those old gauges are unreal how they are supposed to work. They get hot, then turn off, then get hot.......That is how they work. If they don't work they are probably burnt out....On my 66, I calibrated my gas and Temp gauge with a 1K variable resistor, in line, used half tank of fuel, and a known good temp gauge, adjusted the variable resistor, till the gauges read correctly, measured the set value on the variable, with a VOM. Then purchased a resistor to match the value, installed in line, now they work perfect. That is using a home built 5v solid state gauge regulator.