Vintage Cars: Burglar alarm, burglar alarm, high humidity

Question
Hello.
On a 1987 MB 560SEC the burglar alarm has gone into a false alarm state twice.  The first time was a few months ago with weather conditions much like today (cool with high humidity, to the point of condensing drops).  The alarm WILL NOT SHUT OFF using the key-in-the-lock solution.  It sounds for a few moments, then stops for a minute then repeats.
The second occurrence today was triggered when I opened the passenger side door.  The car was NOT locked.
I can't see anything in common except weather conditions and don't know where to look for the problem.  Also, I can't make the horn stop.  
Any insight and suggestions would be welcome just as you have aided me before.
Thank you.
John Dieudonne


Answer
probably a short in the key way connection ( drivers door handle lock) You can remove that and try to locate short, or may just be worn out and need replaced.  I dont think they are very serviceable , but I always try:)  You could try using electrical cleaner on the plugs to the door and relay
Other than that you can just unplug.  To disable the factory alarm system, remove the false firewall in the front passenger footwell, locate the long slim black box with 2 connectors each with about 14 pins, remove either or both of the connectors. The car will run fine with the factory alarm controller disconected