I'm not sure when Some of the 940s started using the Rex-Regina ignition-fuel system. If this car has this system instead of the Bosch, the power stage is part of the ignition coil assembly and not a separate item as with the Bosch system. The coil assembly can be separated and the power stage replaced. In looking around at the on-line suppliers, I not seen even the coil assembly, let alone the power stage. In fact the Regina system seems to be somewhat neglacted by the parts houses. I'm hoping this is because these systems never have problems (ha ha). More likely these systems are in a minority and most Volvos are using the Bosch.

My '93 940 has the Regina system (its made by Bendix). You can tell if your's has it by looking at the air intake and spark coil. The Bosch system has the familiar Air Mass Meter in the inake right naext to the air filter. The Regina has an Intake Air Temperature Sensor at this point and a Manifold Air Pressure (MAP) sensor mounted near the firewall on the driver's side. The Bosch system has the familiar cylindrical spark coil while the Regina uses a squarish unit which combines the spark coil and power stage.

In the case of my 940 (Regina), I'm trying to protect the probably expensive coil assembly by installing new plugs, spark wires, distributor cap, and rotor. Having all these new and set to specs avoids having excessive voltage spikes on the spark system.