It should read several PSI negative at idle. I would look for the MAP sensor, and see if it has a vacuum line hooked up to it. If not, find the line nearby and hook it up. If it does, follow the line till it ends. It should be connected to the LIM somewhere, i think. I'm not hugely familiar with the Series II.
The vacuum T under the supercharger has been known to get quite brittle and crack, so that is a good place to start looking. The MAP sensor is attached to the rear lift bracket back by the firewall. The vacuum fitting attaches to the bottom of it. It can be tough to reach. The 2000+* only have one MAP sensor, however.