I have a 65 conv. Gauges have not worked in 20 years.I replaced the Constant Voltage unit but my temp gauge stays hot with key on but comes back to cool as I turn off power.All other gauges work great.I have replaced the block sensor.

Any ideas
I have had this car since April of 67 I should know this by now.
Charlie B

Disconnect wire at the sensor and turn key to "on". If the guage still reads "H". The wire is shorted out.