You only need to install the plates if its already broken and stuck open. Since they are working and closed you dont need to install the plates. They are closed and will never open with the sais disabled. Just install that control wire and you...
Kind of raises disclosure issues around the sale of the vehicle, like if there are air injection issues were you informed of that fact before the money was exchanged?
I bet when they sold the automobile to you they disconnected the bypass to remove liability from themselves and if left unplugged you will soon see a code.