There are multiple reasons that immobiliser can not be installed in old cars.
First the ecu unit has to be replaced, new ecu unit operate ignition after authentication of the right key code as well as the fuel pump of the car. So that wiring has to be replaced or customized. That is why if some one manage to get control of ignition, the feul pump will not respond.
Then the ignition switch, speedo meter and offcourse wiring needed to be updated again.
So it is not feasible to add immobiliser.
