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Grounded Positive Battery Terminal

Discussion in 'E39 (1997-2003)' started by JC5, Dec 26, 2010.

    • Member

    JC5

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    Just to say right off the bat, I goofed. When changing the battery on my 2003 530 I accidentally grounded the positive battery terminal. There was a nice spark when I did this, and now it seems there is an electrical issue.

    When the car is running at idle, I get 14VDC at the battery, but when the blinkers, window switches and such are used, the voltage drops to 13.4VDC. This can be seen in the various lights through out the car fluctuating (dimming, then brightening). The car never really completely dies due to electrical system failure.

    Is there a a common thing, or point to strart, in trying to locate the source of the electrical fault? Or is this going to be a trip to the dealer? I have a fair amount of DIY experience, so pulling something apart to diagnose will not be a big deal.

    ForcedInduction guest

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    13.4 V would be normal. If under load the voltage drops below 13.0 V with the engine revs up to ~ 2000 rpm, then you may have an issue. 14 V at idle may mean the alternator is trying to charge a discharged or sulfated battery?

    A bad battery cell can also cause abnormal charging rates. If you can test each cell individually thru the electrolyte fill hole they should be ~ 2.0 V each. A bad cell will read low compared to the others or even reverse polarity if shorted.
    • Member

    CRKrieger

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    With your DIY experience, I'd think you'd know this all sounds perfectly normal. If your other lights dim only when you do this at idle, I think there's nothing wrong at all.
    • Member

    JC5

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    It's not dieing, but it didn't do that before grounding
    • Member

    CRKrieger

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    I'd almost bet it did; that you're looking for a problem and you've noticed this more than before. That's perfectly understandable. I know I've done it before. Long shot, you might have fried a fuse somewhere or disturbed a ground cable in the area of the battery. Take things apart; clean them up; put it back together the right way. ;) Quit worrying until something more serious appears.

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