vaccuum line unplugged

found a vaccuum line unplugged on my 00 winstar its a heater line.it comes from the firewall 2 a tee then 2 a end the other end of the tee goes 2 the upper intake.any one know where it goes?

I would expect that the line from the firewall connects to that "T", with one line going to the upper intake manifold, as you mention, and the other line going to a "box" that is on the passenger side inner fender, beside the A/C accumulator canister (aka drier).
This box "holds" a vaccum for when the engine is OFF, to hold the diverter doors in place.

I bet your heater controls quit working as well, right? I had the same line off.... it goes to a black box on back firewall up high cant see it without taking the crowl off..see ford po442 and engine miss by schadd1971 they helped me find where it went