Your problem is that you have it hooked up to the vacuum modulaor vacuum line. That'* right after the throttle body and will never see boost of any kind, only a maximum of atmospheric pressure.
You need to hook the gauge up to either the MAP sensor line or the line that goes to the Boost Bypass Valve Actuator (round black thing near throttle body). It has 2 vacuum lines on it, and one will be the correct one, but I don't have a Series I so I couldn't tell you which one it is. I'm sure someone'll know.