Found a wire, what is it and where does it go?
 

Hey there, I was playing around cleaning under the hood of my new to me, 2004, 3.8, and looks and behold I have a wire that has rusted off its connection and I cannot find anything online or in the service manual to help me out. It comes out of the firewall and seems to want to run around the master cylinder then I am lost, can someone please help.It triggers the check engine light now.
https://cimg0.ibsrv.net/gimg/www.cmo...4cf2eb0ddc.jpg