[70pontiaction]

On my 69s and 70s the thermal switch is located right on the bottom of the air cleaner and measures the air temp around the top of the carburetor, so it senses when the carb is warm enough to idle properly. The vacuum hose that feeds the switch goes directly to manifold vacuum at the small vertical fitting right in front of the carburetor.

The vacuum switch on the intake manifold water crossover turns the vacuum advance on and off depending on coolant temperature. I'm pretty sure it turns the advance on fully when either really cold or really hot (too hot) and ports it in between (normal operating temps).