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Old 09-17-2003, 12:39 AM
Coming back from burnout
Join Date: Jun 1999
Location: in the Pacific Northwest
Posts: 2,274
Replaced alternator, Battery Voltage at 12.0 volts, Red Battery Light on (83 240D)

Did I get a bad alternator? For a few minutes, the voltage read 14.0 volts after I replaced my Alternator.
I took the car for a spin. The red charge indicator came on and when I got home, the voltage was a dead 12.0 volts.
Is there anything else "glitching"? I checked the Wiring Diagram and everything seem straightforward enough.
What the &(((%!! is going on. Iam starting to get superstitious abou this car. My 300D never needs work, but my 240D keeps on breaking down....

Replaced alternator, Battery Voltage at 12.0 volts, Red Battery Light on (83 240D)
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Old 09-17-2003, 10:12 AM
G-Benz's Avatar
Razorback Soccer Dad
Join Date: Apr 2001
Location: Dallas/Fort-Worth
Posts: 5,711
Did you measure voltage with the engine running?

12V nominal is okay with the engine off, but you should get a reading of 13.5 - 14.4V with no accessories on. Anything less and your alternator is not doing its job effectively.

For an early model like yours, you should just be able to replace the brushes, not the whole alternator...

...interesting that you mention needing to constantly work on the 240D but not the 300E...a lot of 300E "fix-me" threads pop up here daily, but most of the forum contends that the 240D is probably one of the most reliable MB models ever made.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car
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Old 09-17-2003, 10:44 AM
Posts: n/a
Hook up volt meter to battery and check voltage. Have some one start the car - check the voltage. Rev the engine to about 1500 rpm check the voltage. If the voltage does not go up when you start the car - most likely bad alternator. But I have had a case where the wire from the alternator to the battery broke internally - so before you condemn the alternator - follow the wire back to the alternator and check the voltage at the wire there with the car running. If it still is not 13.32 volts or higher - the alternator is bad.
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Old 09-17-2003, 10:56 AM
csnow's Avatar
Registered User
Join Date: May 2002
Location: Mass
Posts: 1,127
Perhaps obvious, but recheck electrical connections from alternator and also check for belt slippage.
Suspicious that it worked for a while, then stopped.
1986 300E 5-Speed 240k mi.
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Old 09-17-2003, 12:18 PM
MrCjames's Avatar
California Dreaming
Join Date: Jun 2003
Location: SF Bay Area
Posts: 599
Check your glow plug relay, if it sticks it will effect your output voltage. The one item that is sometimes overlooked when diagnosing charging problems on MB diesels.

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Old 09-21-2003, 11:00 PM
Coming back from burnout
Join Date: Jun 1999
Location: in the Pacific Northwest
Posts: 2,274
The Final Resolution

The problem was due to a bad glow plug relay. The alternator was probably never bad.. I haven't replaced the glow plug relay yet, because its a $100 and I just bought a Robinair vacuum pump, so I do a manual connect-disconnect everytime I start her cold....

Thanks for all your help. dont know how I could do it without you all!

The Final Resolution
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