Where is the coolant sensor on a 1999 Ford Taurus 24 valve v6?

AnswerCoolant LEVEL sensor -

Located on the bottom of the coolant reservoir.

You can see two wire connector protruding towards the fender-side.

It is built into the reservoir tank bottom so whole unit gets replaced.

See "Related Questions" below for the location of the engine cooling fan sensor and the temperature gauge sending unit/sensor.