On the left. Two hose attact to it. It is black with the green top. Screws in to coolant chamber in the manifold.
Its a California model if that helps.
Local parts guys don't know. I damaged it installing the engine.

 

goes to your heater

 

The heater core hoses are much to large to fit on this. They attatch to the manifold at the spigot on the farther left and the water pump.
The bottom of this "switch" is brass and closed. I think it is some sort of a thermo switch similar to the Thermo Vacuum Switch (TVS) that is on the thermostat housing on the right....

 

That's the canister purge TVS. Has to do with the evap canister, which looks about like a coffee can behind the driver's side headlight. Connects to the UFO looking thing that hangs in front of the int man above the water pump.

Since you're in CA you'll need that all hooked up to pass the visual.

That coolant temp sensor, and its wiring, looks pretty much ready to fail at any moment. I'd recommend renewing that as well.

The other thing on top of the water outlet is the EFE TVS. Controls the flapper valve at the right exh man outlet. Should have a big rubber fitting with 2 vac lines going to it. I don't see that in the photo.

Search this forum for "vacuum lines"; your car's is in there. (I contributed it if memory serves ) Fortunately being a CA car doesn't matter to those parts AFAIK.

 

Bingo! Thank you so much. Found new old GM stock on line and ordered it.
Next it that coolant sensor and a hand full of other old broken connectors