Hi all,

My 1982 300SD with 220K miles has a problem. Battery charge warning light was on when the engine turned off, and the battery was drained.

Battery warning light's off when the engine's on, and voltage across the battery went up to 13.77 volts.

Is that problem from alternator or regulator ?

Any help/suggestion is very appreciated.

thang

Have you had any problems with the ignition switch? I don't see how that scenario could happen otherwise.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Thanks for the reply, Sam.

I did not get any problem before that puzzle happened.

thang

Shorted alternator. Shorted internally. Replace it.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

Faulty diodes in the alternator can yield this symptom.

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64 European Coupe Brilliant Silver with Red interior 4 Speed Sunroof
87 TDT 286k
87 SDL 195k
83 SD 202k
83 SD 201k
83 D 286k
02 R1150RT 32K
00 122HP FLSTF
07 KTM 250SX

"Danger takes many forms"

I agree, had a volvo years back that did the same thing, turned out it was a power diode in the internal rectifier. Doides are one-way gates basically, a shorted one lets the battery drain back through itself in reverse.

An easy way to check for a shorted diode is to place you meter in AC while across the battery terminals. If you read a significant AC voltage then you can verify a shorted diode.

(I can see where a shorted stator diode can cause this problem.)

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Sam

84 300SD 350K+ miles ( Blue Belle )

Thanks for all reply,

So, I will buy a new alternator and will let be known of the result.

Thanks again.

thang

Follow-up.

Today new alternator's installed. The problem's gone. Thanks all for the advices.

thang