Automatic Transmission - 4L60E question

I bought a built 4l60e from a guy today that he was using in his 10 sec car but i dont know what this thing is that he added.

it a little nipple looking thing right next to the big green electrical plug on the side. I bought this from a guy but it was actually his son's tranny so he wasnt sure what the nipple thing was either.

Someone please help....Can i just cap it off or what?

Thanks in advance

No its using a vaccume modulator to control pressure you will need to hook manifold engine vaccume to it

So i cant just cap it off and let the trans run off the electrical stuff for now or will it not even work if i dont hook up the vaccum??

Also just wondering but why is this better than using electronics? and what pressure is it even controlling (the valvebody pressure or what)? Excuse me for my lack of knowledge on transmissions

It will shift, but without it hooked up to vacuum, you will have "full" line pressure all of the time and this will destroy it. Hook it to a "tee" in the vacuum brake setup.