No idea what this is? In the first pic you see it sits between my throttle control relay and fan relay. Not show in my picture, but there is a vacuum hose that fits on the top black neck and runs to a vac port on the intake manifold that is behind the carb and in front of the distributor.

The next picture is of the top of it where the vac hose goes. No hole in the top from what I can tell. The third picture is of the bottom some kind of white stem that had nothing hooked to it and a plug for a single wire.

I found reference to it under the following post under response #18 and #19 along with a pic. It is spoken of as being a check valve for accessories. No idea what that means or what it does. I have seen it in pictures on other TA's besides mine, so I strongly believe it is factory.

https://www.thirdgen.org/forums/tech...-pictures.html

Some thought it might be to the hood scoop and my guess was maybe cruise control, but all seem to be wrong. Also the MAP (differential pressure ) sensor is sitting behind it along with the A/C relay. What could it be????

 

Here is another pic from a member's post. His car is an 83 and you can see whatever this thing is on his car as well.

 

Transmission converter control vacuum switch. Uses ported vacuum to control lockup of the torque converter, along with input from the brake pedal vacuum switch and a 12V signal. If you check the wiring to the plug it should run to the transmission 3 wire plug, the brake pedal switch as well and a fused 12V source.

 

But my car is a factory T-5 manual transmission, no torque converter. I found another pic of a 84. It looks like this thing might be running to a cruise control.

 

Vacuum switch for the cold-air induction hood.

 

^

 

Any idea how this switch works. Is there suppose to be something plugged into the bottom of it?

 

The flaps in the hood were solenoid operated, turned on and off by the switch to open when there's low vacuum.

 

I agree, I forgot the 84 Firebirds still had the functional hood scoop, unlike the Camaro's that went to non-functional steel hoods in '83. That vacuum switch can be used for either, I've found them in full size trucks used for TCC control (and what I currently use one for). I've never seen one used for induction control (not disputing it, just never ran across a functional induction-equipped car!) , but I imagine it works just as well in that purpose.

 

No vacuum lockup on a thirdgen. Lockup is electrical.

 

Already been identified, see the above posts, thanks.

 

Yes, it's electrical. That's why non-computer thirdgens came with electrical vacuum switches.