Coolant level sensor?

The Low Coolant Sensor should be located on the right-hand inside of the radiator about a foot down. Just lean over and look below the radiator cap. You should see a fixture with a cable attached.

Just unplug it if you want the light out without replacing the sensor. You must drain some of the radiator in order to replace the unit. I believe this model has an o-ring and screw replacement. Some models are a "screw-in" type.

An aftermarket version will probably cost you about 35-40 dollars.