I don't have the wiring diagram in front of me, but I doubt it would be much help. The sensors on the 850s (which are the same) go bad all the time. The fault tracing for them is to check the ground and check for battery voltage on pin 2. If those are present, the sensor gets replaced. I have never replaced an ECM for a CMP code but I've replaced dozens of CMPs so I would certainly start there.
Volvo doesn't give us a spec for that in the fault tracing of that code. If you'd like, I'll check the voltages on my car (95 850) tomorrow and let you know- they should both be the same.
Here is the wiring diagram. The CMP is 7/21. As you can see, there is no indication at the ECM pins 10 and 8 as to what the wires do. Payment has been released so I will follow up with you tomorrow when I measure an actual 960.