[RicksGTO]

your '72 should have a thermo-vac switch with just 2 ports, one on the side that goes to the carb. and one on the top that goes to the carb port of the charcoal canister. Here's a pic of a correct switch I have for mine, it's GM part #3026085, they are discontinued but one comes up on eBay from time to time. I think they were used on several other '72 engines so you might come across one on another car, etc. Also a pic of Lloyd's a/c auto car I have saved that shows the rounting from the switch to the charcoal canister for an a/c car. Your's may or may not have the cad plated bracket to guide it if it's not and a/c car. Maybe someone else will have a pic of the diagram from an assembly manual.