Question about 1984 BMW R 80
The first thing I would check is the rectifier. This is what turns the AC current from the generator into useable DC current for the bike's electrical and battery charging system. A faulty rectifier will cause the problems you describe; dead battery and excessive sparking when connecting the battery.
The rectifier can be checked using an ohm meter. Basically, there are six diodes inside the rectifier which should each show zero - or very little - resistance one direction and infinite resistance when the test leads are reversed. It might be easier to take it to a dealer to have tested.
Posted on Oct 27, 2009
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