Question about 1984 BMW R 80

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I tried to start my motorcycle and out of the blue the battery was completely dead. I had it running the day before. I disconnected the neg cable and fully charged the battery. I went to connect the cable back up and got lots of sparks. Do you have any ideas. My brother said it might be the magneto.

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Wayne Thomas

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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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