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I have a '81 300SD and the battery won't hold a charge. I had the battery tested twice and it is fine and I disconnected the positive cable and the car kept running just fine eliminating the alternator. The cables and posts are in good condition - no corrosion. Anything else it could be? I can drive the car for a day or two until the battery goes dead. If the battery and alternator are fine I can't think what else it would be.

Thanks for any help!

Patrick
 

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1986 300 SDL Turbo
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Can't remember where but,
I read about a car with a bad glow plug relay which left the plugs on all the time, drained the battery.
Maybe?
 

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w126
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A diesel doesn't require electricity for fuel delivery(as a rule) or ignition. I'd pull the alternator and have it tested as Teutone suggested.
 

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is your alterator producing any juice first? when running should be > 12 -13.5 i have seen as high as 14v

some suggest run a test light or bulb in series with cable and battery , if the bulb lights up means something is drawing current.

For my diesel truck i did bought 2 of these battery switch, un-screw = no juice passing, I turn both off when i par for days. Is dual batt so i need 2.
If i keep driving the same day i dont need to unscrew, only when i park at night.

I guess your batt is holding the charge too.

Alt could produce no power too.
 
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