I don't see how a simple short in small gauge wiring can destroy a battery like that. Something else must be going on because if the power drain was enough to completely drain the battery, it would have started on fire.
Start with the basics. Make sure the alternator is charging. Check the battery for at least 13+ volts with the engine running. It sounds to me as if your alternator is not charging and the battery simply lasted a few weeks without being charged until it finally gave out.

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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