Can anyone tell me how this Ported Vacuum Switch should be connected on my 69 350 cutlass and what it does?

 

The purpose of the ported vacuum switch is to control the advance at the distributor based on the operating temp of the engine. You should have three ports on the switch. The top port goes to the advance on the distributor. The middle port goes to the ported vacuum port on your carb. The bottom port is connected to manifold vacuum via the port forward and to the left of the carb. If you have an auto trans then there should be a "T" from the manifold vac also feeding the modulator on the trans. Have a good one.
Kevin