[avisitor]

Looks like a windshield sensor
When it rains, the rain falls on the windshield
And blocks some light from getting to the sensor
If enough light is blocked then the wipers will turn on
If it is totally dark the wipers do not turn on
But, those sensors are usually up higher on the windscreen
And behind the rear view mirror

So, guess it must be used by the HVAC system??

 

[avisitor]

I would assume from @AUTOSPARK 's comment that it serves as part of the temperature control unit