An NA motor sucks air through the intake manifold. A turbo, on a turbo motor, pumps air into the intake manifold and builds boost. So an NA motor will always mark negative on a boost guage. A turbo motor on the other hand works the same way as a NA motor at lower RPM and shows negative too. As the RPM goes up, the turbo spools and builds boost, it will start to go into the positive at a certain point until you get the full boost reading. Which is whatever you set your boost to. That is why you see negative at low RPM and it goes toward the positive at higher RPM. As to your problem, I don't have much experience with turbo motors yet. Sorry.
Marcos