I don't know if I can adequately describe how the vacuum control switch works, but I will try. There are seven vacuum nipples, one of which is connected to engine vacuum, the others to the various actuators. Behind those nipples is a sliding plastic block sealed with grease against the backside of the seven vacuum ports/nipples. As you move the selector, the lever slides the plastic block back and forth changing which port gets engine vacuum. On the side (top or bottom, I forget) of the sliding block are three ramps which ride across three electrical contacts. This changes which plugs on the five-way electrical connector are live. Off of the main vacuum harness, one of the hoses tees off and connects to the back of the heater controls to provide vacuum to the variable control from which the the other hose goes to the water valve.

The vacuum nipples get brittle with age and break off.