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2014 Mercedes-Benz GLK250 Bluetec, 1981 Mercedes-Benz 300D W123
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600 Posts
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My mechanic replaced the original alternator in the 300D turbo diesel. Said that the alternator connector was covered in green corrosion. Installed the Bosch re-build in Germany alternator. Said he cleaned the connector before he plugged it back in. The battery light was not on with the previous alternator before, but I noticed that the charge rate was very low. So, with the new alternator installed, the battery died again after my friend left the side marker parking lights on for an hour.. jumped it started up and drive 28 miles.. no battery light got home battery was still dead. would not start.. Went to Mercedes dealer, bought a new battery. I have been driving it around ALL day and I don't know if the battery light was on due to the brightness of the sun. Tonight after dinner out, it was dark when I was leaving, I started it up and the battery light slowly came on VERY dim and I stepped on the accelerator for a second thinking it would go away, but it did not. when I got home, I left the car running, grabbed the volt meter. Was only reading 12.70 volts and did not change when I revved the engine. Also, there is a crummy connection on the positive line running to the battery.. wrapped in electrical tape that looks like it was done by a previous owner. With the original alternator, with the volt meter I could rev the engine and it would show that it was charging. What could this be? :confused:
 

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1984 300D
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5,070 Posts
Do a better job fixing the Wire and see what happens.

From what I have read these Alternators need to have a good 3 watt Bulb in the No charging light to work.

The need to have excellent electrical connections to inclued the Chassis to Engine Ground Strap and the Battery to Chassis Ground Strap.

Some people have even run a Separate Ground Wire from the Battery to the Altenator Casing. Why, because Rust where the larger part of the Alternator Bracket bolts to the Engine can mess with good conduction.

The Alternator Connector can come apart and you can inspect and clean the Connectors. They also show the Plastic part of the Connector and the Metal Parts in the parts Catalog. I don't know if they are stocked.
 
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