Panic/ alarm system on 97 Thunderbird

When the driver's side door is locked, the horn will sound and lights will blink repeatedly. At this point the only solutions are to leave the car unlocked or take the battery cable off. Is there a way to disable the alarm system without disabling the horn?

Has the car been hit? Did this problem start after being hit or after someone was working on this car? There is an inline fuse holder in the left side of the trunk that has a 20A fuse in it for the anti-theft circuit. I don't know if removing it will stop the lights and horn but you can try it. Are you locking the door with the key or remote? There are various switches throughout the car that the anti-theft controller monitors. The switch position of any one of these can cause the horn to sound and lights to flash. More info from you could help.