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Old 05-29-2005, 02:41 AM
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Join Date: May 2004
Location: California
Posts: 30
84 300D Dead Battery w/ Battery Light Fade in/out

The 3 month old battery was dead this morning after trying to start. Plugs glow, just not enough juice to start. I have noticed recently upon start up, the battery light fades on during normal idle speeds until I give it some "gas" pedal to speed up idle - then the light fades out. Is this an alternator issue? The alternator seems to put out 12v. I am stumped. Recent addition of an aftermarket stereo...noticed the light fade in and out sometime following the install. Related?

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Old 05-29-2005, 02:49 AM
Senior Member
Join Date: Jun 2001
Location: Northern Calif. (Fairfield Area)
Posts: 2,225
It sounds like alternator time and specially if you are reading only 12 volts. To be accurate you should use a digital volt meter. A fully charged battery reads 12.6 volts. With the engine running, you should measure at least 13.2 volts across the battery which is alt output. If you are reading 12 volts, the alt isn't working and the battery is dead.

Auto Zentral Ltd.
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Old 05-29-2005, 11:02 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
Most likely the voltage regulator brushes are worn off -- I've replaced four or five of them over the years on European cars, always the same symptoms -- battery gradually goes flat, headlights are dim/flicker, no increase in brightness with rpm increase, and the alternator lamp glows dimly. Usually can't see that except at night.

Voltage regulator is about $30, two screws, dead easy to replace.....

If the alternator is noisy, replace it. Just did the one on my brother's 300D. He broke a two year old belt on the highway, limped home and was installing a new belt when I stopped over (he's had neck surgery and has some serious limitations on neck movement now) -- I spun the alternator and it squeaked with the belt off -- time for a new one!

1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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Old 06-13-2005, 12:29 AM
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Join Date: May 2004
Location: California
Posts: 30
Turns out it WAS the alternator

Installed a new Bosch voltage regulator and that did not solve the problem. . I spent about three hours under the car attempting to remove the alternator and wass unsuccessful. Turns out the tension adjusting bolt was bent. I had the car towed to my local indy and had them R/R the alternator.

Anyone knopw what to do with my dead core? The Ebayer did not requier a core exchange. Does anyone buy this or is it trash.
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Old 06-13-2005, 03:52 AM
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Join Date: Oct 2004
Posts: 482
Keep it. You never know when it will come in handy.

Say that the new alternator falls out on the road for some crazy reason. Well, now you still have a core when you need a new one!

I'm a pack rat, so I can rationalize keeping everything.

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