Which wire do we cut to deactivate the car alarm.

If it were that simple any car thief could do it. Factory anti-theft systems are real effective at keeping owners out of their cars, and GM's are some of the best. There's nothing you're going to disconnect or remove. A signal must be generated to tell other computers on the car to turn on. Without that signal the engine won't run.

If your security light is on solid or flashing most likely you have a bad ignition switch there under 30 and easy to install. If you have a code B2960 and or B3033 bad ignition switch.