Battery light - Mercedes-Benz Forum
 
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post #1 of 6 Old 09-19-2005, 11:45 PM Thread Starter
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Battery light

I have a 1985 300SD. For some reason, with the ignition on but motor off, the battery light no longer comes on. And then when i start the engine, the light glows just slightly. Sometimes it gets bright, other times it gets really dim. The odd thing is that the lights work, and the engine starts up no problem.
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post #2 of 6 Old 09-20-2005, 06:17 AM
 
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Sounds like you have a bad diode- does the alternator charge while running?
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post #3 of 6 Old 09-20-2005, 04:12 PM Thread Starter
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Don't know yet, i need to have my dad bring his meter home so i can test it. It was odd because today, i had no problem, drove it to school and the battery light didn't come on. Is that diode that your talking about part of the VR?
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post #4 of 6 Old 09-20-2005, 05:49 PM
 
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The diodes are within the alternator.
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post #5 of 6 Old 09-21-2005, 11:07 PM Thread Starter
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Well the car is starting but it's cranking much slower, so i know the battery is losing power which tells me that the alternator isn't holding a charge like it's supposed to. Hopefully if my dad brings his meter tomorrow then i'm going to test that out, and probably check out some other stuff just to make sure. There's a guy in town locally that rebuilds starter motors and alternators, i'll make sure to tell him to look at the diodes in the alternator. Thank you for the response.
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post #6 of 6 Old 09-22-2005, 05:34 AM
 
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Be sure to check the voltage regulator before you replace the alternator. Often the alternator is good and you only need a new voltage regulator to fix the problem. That is a much less costly fix.
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