I find the switch to disable my immobilizer on a 1992 Ford Falcon?

There is no switch to disable the immobilizer system on a 1992 Ford Falcon. Ford didn't introduce widespread factory immobilizer systems until much later than 1992. Vehicles from that era relied on other anti-theft measures, like ignition locks and possibly aftermarket alarms. If you're having trouble starting your car, the issue is likely something else entirely, such as a faulty ignition switch, battery, starter, or a problem with the car's electrical system.