Try to unplug the wires at the sensor. If the light goes out, it is a bad sensor. You can also use an Ohm meter to measure its resistance to determine if it is bad. But I forgot the numbers. I faintly remember that it should close (zero Ohm) when coolant level is low and open (infinite Ohm) when coolant level is high. Do not quote me on this as I di dthis a while ago. The factory manuls have the numbers.

The sensor is easy to replace and inexpensive. About $15.