The ignitor is just a transistor ignition unit. It takes four low-current inputs and outputs high current for the coils.
22020-85M10 TRANSISTOR IGNITION UNIT Mitsubishi
* 1987-1988 KN13 USA "Sentra XE" CA16DE/CA18DE
* 1987-1988 N13 Pulsar NX CA16DE/CA18DE
* 1990-1994 Q45 V8
22020-60U00 TRANSISTOR IGNITION UNIT Hitachi
One input plug has 5-wires -- 4 inputs low current triggers. The odd pin is for ground/earth.
The other plug has 4 high current outputs to the four coils.
The SR unit is smaller, newer but works the same way.
* Nissan 22020-50F00 'DIS4 04'
A common, cheaper replacement is the Bosch 211 Ignitor, used by many cars for example VW/Audi.
See
Coil On Plug