Mercedes-Benz W126 battery drains and alternator does not charge
280 SE300 D
Why does the W126 battery drain overnight?
The cause can be an alternator that does not charge at all, or the wire of the auxiliary fan installed in front of the radiator for the air conditioning. A hot wire indicates a leak even if its 25 A fuse has not blown. The voltage of a running alternator is about 14 V.
The alternator is not charging - what is a common cause?
The alternator brushes may be completely worn out. They can be replaced with the alternator in place by removing a couple of screws at the back. The voltage regulator should be replaced at the same time. If the alternator is old and not charging, replacing the alternator fixes the fault.
The charging light stays on and the lights dim at idle - what is wrong?
Oxidised connectors behind the instrument cluster can cause a poor ground. Cleaning the connectors has fixed the symptoms. Replacing fuses has also removed the cluster symptoms.
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