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Old 07-02-2003, 09:52 AM
K Juul
Posts: n/a
380SL Charging problems

Looking for help troubleshooting a charging problem. The car runs fine, no Batt light, however seems to discharge the battery as it is run. Took it to Auto Zone, they did the load test on the Battery, said it was fine, except battery was discharged. Jumped the car to get it restarted, they checked the alt, voltage was 13.5, but charging amps were low, about 20. Replaced the voltage requlator, the brushes were about half worn. The overall condition of the alternator seemed ok for an 18 year old car, did not see any diodes to check, are they inside? Charging voltage now is still about 13.5 which seems low, haven't had a chance to check the charging amps yet. I have the MBUSA CD, information on the charging circuit is very slim. Are there any fuses/relays/links that need to be checked? Any known problems with the battery in the trunk? As I sit at work writing this, I can't say for sure that the battery light comes on during the prestart light check, but I didn't notice that it didn't. I know on my BMW, if the light is faulty, it disables the charging circuit. Is that true in this case? Hope to drive the car over the holiday weekend, help please!
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Old 07-02-2003, 11:37 AM
Registered User
Join Date: Sep 2002
Location: Newcastle upon Tyne, UK
Posts: 215
The dash board light is part of the circuit, so check that first. However this is an all or nothing thing.

Low output can be down to a blown diode in the rectifyer, but I think this is integral with the regulator, so that's not it.

So you're left with simple stuff to check, tightness of drive belt, clean and tighten connections on alternator, battery and ground straps.

If these are all OK, you could have a problem in the windings of the alternator.
Cheers, Neil
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Old 07-03-2003, 12:35 AM
Senior Member
Join Date: Mar 2001
Location: Accokeek, MD
Posts: 683
Also make sure the inside of your battery cable clamps are clean. Altenator cannot charge without proper load which requires good contact at battery and other grounds... engine to body... as mentioned in previous post.

1993 190E 2.3
2000 Toyota 4x4 Tundra
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