So I just took my front end off and replaced my alternator and serpentine belt. I am in the process of putting it all back together, but I can't figure out, or find anything in the forums, about what this is and where it goes. any help?

 

Which car is this off of? That is your outside temperature sensor. Usually mounts in front of the PS Cooler / Condenser

 

It's a 2001 s4. Thank you! That helps a lot.