86' 300zx security trouble

Not going to fix your current problem i think, but might help with future problems. something was wrong with my alarm and only the security light would light up, which drained my battery daily =) I just took out the fuse for the security system and haven't had a problem since.

Just unplug the alarm box under the seat or pull the fuse. Like someone else said, just disconecting the battery should deactivate the alarm. Unless your brother did something inside the door that makes the alarm think it needs to reactivate itself? EVen so if you unplug the box, the car should work fine.