call MBNA USA and purchase the little booklets that orig came with the car, did yours not come with any? check mag pockets behind front seats.

My W126 was doing similar alarm symptoms and I did all the things the booklet said, like put master key in drivers door lock and reset, did not work, had to disconect alarm plug underneath passenger foot rest.

Also at MBNA order ALL of the Service CD manuals for your W140. electrical, climate control, error codes also.

Get yourself a good multimeter and an OCB scanner for the codes. You are going to need these.

Your car is a 92, does it have R12 freon or 134A?

__________________
1993 Mercedes Benz 300D 2.5 205K (ex wife's)
1984 Mercedes Benz 300SD 320K (SOLD)
2004 Mercedes Benz C240 75K
1995 GMC Sierra 2WD 5.7L 188K
1983 Mercedes Benz 300SD 239K (SOLD)
1987 BMW 325i 220K (SOLD FOR SALVAGE)

609 Certification