The Immobilizer.
The picture below shows the transceiver or aerial. This is found behind the steering cowl. The ring sit’s around the ignition switch and is held to the steering column with one screw.
This is the wiring plug.
It needs cutting from the car with as much wire as can be pulled free.
Retaining clip shown at the bottom.
There are four pins, They may be colour coded as above or they may be all black as shown in the photo. This depends on the age of the donor.