The "Collant Low" light on my dads 92 Park Avenue will come on and stay on. We checked the coolant in the radiator and in the overflow tank and both are filled to where they should be. This will only come on usually in the morning or when it is cold outside. It has been doing this ever since our mechanic changed the Water Pump in the car. Any ideas on how to correct this problem?

The sensor is located in the radiator on the passenger side, facing the engine. Try simply disconnecting it to see if the light goes out. If it does, the sensor is bad.