Round Plastic ball under air box

[bmj121]

So, in my search for the horns, I discovered a round plastic ball roughly the size of a softball on my 1997 Ford Explorer. I wouldn't care, but it was just dangling there, unattached to anything except two wires that went into it.
So can anyone tell me what this is and where the hell it's supposed to be attached?

Also, I can't find the horns.

This is my first post, so if I messed up on protocol, go easy on me.

 

[weh87]

As for horn I wanna say check under battery tray I'll double check when I get back to mine and I'll look for the ball.

 

[scdix50]

The round ball is a vaccuum chamber. Should be attached to the interwell under the air filter. It has to do with heater control at the output side of the water pump.