APC system STILL doesn't work HELP!

I still can't figure out what the problem is with my APC system. It just doesn't want to allow anything over basic boost. I recently bought a complete APC system that came off of a working 89' Saab 900 Turbo, just like mine. I have fitted everything I got from the other car and it still didn't want to work. I currently have a MBC connected and I don't like it (boost is all over the place) but I can't figure out what the problem is with the APC. The wastegate works great and holds pressure when the vacuum line was disconnected. The only visible problems I have noticed is that the seat belt light blinks because the fuse was pulled (passive seat belts don't work) and someone removed the housing for the oil filter and replaced it with the N/A housing so I can't connect the oil cooler to the engine. I can't think of anything else to do or what it could be! The APC solenoid will click when turning on the car as well as when I apply the brakes. I get a series of clicks when tapping on the knock sensor. I have two of everything related to the APC system and have replaced everything and still nothing. What else could cause it to run in base boost????? What color are the wires that go to the boost sensor under the dash?