What is this part and what does it do?
 

1975 TA. Sticking out of the shaker assembly on passenger side.

TVS Thermal Vacuum Switch. Has different uses on different models. Simple setup is a vacuum line to it and runs to something else, but its operation is temperature controlled, either to work only when cold, or to not work when cold. In 1975, I think it diverted to the secondary vacuum pull off. In other models it also ran to the snorkel diaphragm for cold starts.

Thanks for such a through answer exactly what I was looking for.

Hmm. Pic is the size of a postage stamp. Barely can see