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Padlocking the auto shaft is for cars the require you to lift up the lever to change gears, you put the padlock in so it can be lifted up and the gear changed. If your auto shifter has a button that needs to be pushed in the padlock isnt going to work
To make the car un startable, Pull up the console, work out which switch is the park switch ( the one that stops you starting the car in D and cut it, Put a momentary switch in and everytime you start you just have to push it
Ben