Hi,
For anyone wondering what that little black vacuum hose connector is on the rear of your 68 Skylark manual Htr/Vent/AC/Rec switch its nothing more
than a soft rubber adaptor that shuts off unused port number 4 on the switch. If it becomes damaged or rots with age, simply remove it, fashion a
suitable plug (piece of hose w/a plug in it) to close off port #4, and connect the vacuum hoselines to the corresponding port numbers on the rear of the switch.
Position 1 has a "T" on it. One side goes to the master vacuum switch on the heater blower speed control switch, and the other to the outside air/recirculate
vacuum motor behind the passenger side kick panel.

Tonino