Charging system 78 300cd - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 12-16-2015, 07:21 PM Thread Starter
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Charging system 78 300cd

Hey guys so I got a 78 300cd, and the charging system in it has been acting strange lately. I've replaced my battery and alternator recently, but my little battery light keeps coming on while I'm driving. It started happening after I accidentally left the key in the on position after getting out of the car a week after replacing the alternator. So I'll turn the key to the pre glow, battery light comes on along with brake. Turn the car on, after giving it a bit of gas it dims a bit. And as I'm giving it has it fades away, and while breaking it slowly comes back. It kinda blinks while idling. I came on here looking for an answer, and most people that were having the problem were saying that it was my alternator regulator. So I went out and got a Bosch regulator, that fits my Bosch alternator, and put it in and the light still comes on. I'm not really sure what to do cuz I feel like I've gone through the whole system now, but I'm probably wrong. Any advice would help.
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post #2 of 3 (permalink) Old 12-17-2015, 09:21 AM
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The problem could be a bad diode within the alternator.

You can have it checked, sometimes free. Mind you I have autostores tell me my alternator is bad when there is nothing wrong with it. So be varefull where you go - proper auto-electric shop is best.

Another possibility, is slipping alternator belt.

This link explains how most Bosch charging systems work:

Bosch Charging systems
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1972 350SL 4.5L - MBGraham, near Kingston, Ontario
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post #3 of 3 (permalink) Old 12-30-2015, 08:15 PM
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It could be possible that the idle speed of the engine is a bit low,all what`s below 700 - 750 RPM might let the battery light come on,too...
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