I am trying to use the Saab APC system on my 89 745T automatic, but the results are confusing. The only way I have been able to get it to work is by disconnecting all the inputs except for the pressure transducer. This is my second transducer which measures about 12ohms at rest, 9ohms at vaccuum and a max of about 100ohms at fuel cutoff,the first transducer measured infinite ohms at any pressure/vaccuum and was obviously bad. With only the transducer connected and the pots readjusted, I am able to run the boost pressure to 12-12.5 lbs at WOT, just below the fuel cutoff, which is where I want it. However if I connect the knock sensor or the neg coil connection ( either or both) then boost pressure drops to the base 7.5 pressure. I can do without the rpm mapping if necessary but I would like the anti-knock protection feature of the APC. The ECM is a Saab #7524135 and I wonder if this is an early black box that cannot handle the electonic ignition. This theory however does not explain the knock sensor problem. If I connect just the knock sensor (not the pressure transducer or the ignition connection) the boost is raised but naturally with no upper limit because of the unconnected pressure transducer, I keep hitting the fuel cutoff limit at WOT. The knock sensor wire had been cut by the salvage yard but I reconnected the two inner wires and the outer ground shield. The inner wites show low impedence to the plug, the shield is impossible to measure as there is no connection at the plug. Could this wiring be the problem? My power is being drawn from the positive side of the coil and the 3way valve seems to be functioning normally. I don't understand what the problem is. Does anyone with APC experience have any ideas how to get both the pressure transducer and the knock sensor to operate correctly?