87 300D Car Alarm Stuck

[Ockman]

My friend has a 87 300D and his factory alarm is on and he can't turn it off other than to disconnect the battery. He hoped disconnecting and reconnecting the battery might recycle the system but that did not work. He does not have the original key for the car since the ignition switch was changed and does not have a plastic key which is mentioned in the owner's manual. Any idea on how to disable it or reset it with the info provided? (Tried in Tech Forum with no luck.)