I have a 2005 Tahoe, and cannot figure out what a wiring harness is for in the engine compartment. It is on the firewall passenger side. It is just hanging there coming out of a wiring harness. It is right next to the A/C evaporator. It is a blue weather-tite connector, and has a brown and a black wire coming out of it. I'm assuming it is some "check port" but I don't know. I bought the Haynes service manual, and it doesn't have anything on this. Any ideas?!?