First thing I'd do is put a battery disconnect in it so you can at least have a driveable car and can fix it at your leisure. Those switches cost maybe $10 and can be installed in a few minutes. Once I started diagnosing, I'd put the meter between the +post and the positive cable to measure draw and remove the fuses one by one until I found the circuit that was causing the draw.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13