1981 Vacuum Line identification
 

Trying to make some order of this birds nest of vacuum and electrical wires under the hood of my 81. Stock minus the Air Pump and EGR hardware, Need so help identifying the small hard vacuum line in these pics. Specifically what is it for and where does it connect to. The other hose that Tees off goes to the double check valve line to the carb. Thanks in advance for any assistance.
https://cimg2.ibsrv.net/gimg/www.cor...93aba165ba.jpg
https://cimg6.ibsrv.net/gimg/www.cor...56c491d706.jpg

It's the HVAC system vacuum supply and runs to the mode selector switch.

Thanks Mike. Anyone have a pic of routing and where it goes through the firewall. I have the service manual and the factory assembly manual but not the index. If there is a page reference it would be much appreciated.

https://cimg4.ibsrv.net/gimg/www.cor...f1bfa8706b.jpg

If you need a good picture for how those lines are to be routed from the factory, purchase a copy of the Assembly Information Manual (AIM) for your year. If you intend to work on your car, that document is a MUST HAVE.