I had to disable mine and it was one of two electronic "packs" in the Right Rear Fender near the fuel filler tube. There was a cable with a large plug on it that was simply disconnected. I think the other "pack" next to it controlled the door locks.

I disabled mine because the alarm would trigger for no reason on warm sunny days.

I hope this helps and I presume things didn't change between 1990 and 1992.

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02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)