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1983 240D
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27 Posts
Discussion Starter #1
Ok, I am new and I searched for the exact same problem and didn't find it anwhere on the forum. If someone already had the same problem please reply with the link.

So, my alternator is rebuilt, and my battery it charged. Verified the alternator is working right and the battery was charged with the auto parts store test by the tester that clips on the battery terminals. Shows they are working right, except it gave a vague message there is some other electrical problem.

When I start the car, the battery light stays on after I start until I rev the engine. Then the warning light goes out and stays out. Every time the same.

Got the manuals from Mercedesmanuals.com so I have the full circuit diagram, I am just wondering if anyone has a troubleshooting guide, or perhaps a few simple things to check. I am not advanced enough to work off the diagram alone.
 

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1983 240D
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27 Posts
Discussion Starter #3
123 Benz said:
Sounds like the belt needs tightened.
Belt is on there pretty tight. Don't think there is any slippage. I don't have the mechanic's tool, but I can only deflect it on the longest span by a centimeter or two.

Do ya'll still think I have by belt wrong? I think it's good. Any other ideas? I am hoping someone has a step by step troubleshooting guide.

thanks.
 

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366 Posts
Sounds like the "exciter circuit" on an older VW; the alternator doesn't start charging until the engine has been revved past 1500 rpm. It is probably your voltage regulator.
 

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1981 300CD, 1973 280C
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448 Posts
You might verify the engine to chassis grounds are intact and clean and tight. Should be one from bellhousing to frame on passenger side.
 

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Registered
1983 240D
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27 Posts
Discussion Starter #6
carnut1 said:
You might verify the engine to chassis grounds are intact and clean and tight. Should be one from bellhousing to frame on passenger side.
I cleaned the battery-to-chassis to battery terminal connections and tested them with an ohmmeter and for voltage drop. Both are perfect- light still comes on as described above.

Lorbenzo Lammas said:
It is probably your voltage regulator.
I will check the voltage regulator first.

I also spent time yesterday reading the factory instructions for electrical testing. I feel more confident that if I carefully walk through each circuit with my multimeter and jumper cables I will find the problem(s).

I still appreciate any suggestions and I will post whatever I find.
 
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