vacum hose question

[Torque]

The puzzler is at the rear of the engine(pass. side)Two vacum hoses are fitted into a plastic Tee.Where does the third arm go to?The two hose join two S/steel pipes that run back towards the transfercase.What I see is a pluged port on the intake manifold and also a port at the base of the carb(Motorcraft 2100 2bbl)located pass. side towards the front.
Thank you for any info

[andy d]

there is a vacuum controlled flap on the air filter housing getting vacuum fromm somewhere back there

[Torque]

Thanks Andy,
On the air cleaner I've got the heat sensing switch at the base and was wondering what
the 'whatchmacallit'on the side of the air cleaner housing was for now I've just got to eliminate as many vacum ports as possible and see what I'm left with.Can anyone tell me if its just a straight vacum or does it have to be routed through a transducer or ampliefier of some sort?