Central locking (central door locking).
The imobiliser is the 2 wires at one end of the white plug, beyond that I still don't know much.
You might be able to retro fit a central locking system, either an aftermarket one or the late '80s RRC unit. neither of which need the factory alarm.
Alternatively If the door motors are 5-wire you should be able to wire up the central locking on it's own.