Ford Repair: Low Coolant Light, radiator coolant, temperature gauge

Question
The low coolant light comes on within a minute of the vehicle starting up.  The engine does not get hot and runs fine, the temperature gauge is normal.  I changed the radiator coolant and no change.  Do you know where the sensor is for the low coolant?  The overflow reservoir is at the normal level and is OK, I have detected on leaks.

Answer
The coolent sensor needs to be changed.  It's giving fault signal since all physical evidence are good!  

I need to know the car model, year etc.. to help locate the sensor.  I recommend that you go to an Autozone and have them read the code (free service) to confirm as they can help locate the sensor.