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1998 ML320 (W163)
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Discussion Starter #1
I installed a "new" (remanufactured) alternator yesterday because my old one stopped charging at idle. Now, I have no charging at all. I checked the nuts on the back of the alternator and they're very tight. Is there anything that I may be missing? I checked in the fuse box for any fuses with no luck, is there a hidden fuse somewhere? I did disconnect the battery prior to touching the alternator so it couldn't have grounded out somehow. The old alternator was in fact charging, I just had to rev the engine after starting to get the voltage up, and it would stay where it's supposed to be.
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Alternator source? Part number? Link? Connection at big alternator lug does not look that clean. What about small wire, terminal 61?
 

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1998 ML320 (W163)
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181 Posts
Discussion Starter #3
Alternator source? Part number? Link? Connection at big alternator lug does not look that clean. What about small wire, terminal 61?
It was a Remmy alternator from RockAuto, only alternator I could find with the pulley already installed, and it's a remanufactured Bosch. I can spray it with some brake clean and see if that does anything, they were clean when I put them on though, no dirt or anything like that.

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2003 ml500, 2004 ml350
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Have you put a volt meter directly to it check output?
Also how is your battery? a bad battery can short and wreck havoc with an alternator.

You would not be the first to get a bad unit out of the box. Not for the ml but had one go bad 2 weeks after install.
 

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It was a Remmy alternator from RockAuto, only alternator I could find with the pulley already installed, and it's a remanufactured Bosch. I can spray it with some brake clean and see if that does anything, they were clean when I put them on though, no dirt or anything like that.

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It is not about dirt but tarnish. Those high amp connections at alternator and starter need to shiny.
Does battery warning light come on with key in position 2? Alternator needs external exiting current to start charging. That current is provided by terminal 61 (D+) small wire.
 

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1998 ML320 (W163)
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181 Posts
Discussion Starter #6
Have you put a volt meter directly to it check output?
Also how is your battery? a bad battery can short and wreck havoc with an alternator.

You would not be the first to get a bad unit out of the box. Not for the ml but had one go bad 2 weeks after install.
Battery is fine, less than two years old and had no prior issues. I haven't put a bolt meter directly on it but the battery is sitting at 11ish volts with engine running and charging for a few hours last night.

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1998 ML320 (W163)
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Discussion Starter #7
It is not about dirt but tarnish. Those high amp connections at alternator and starter need to shiny.
Does battery warning light come on with key in position 2? Alternator needs external exiting current to start charging. That current is provided by terminal 61 (D+) small wire.
Battery light is not on in position 2. How do I test the small wire?

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Your battery should be reading more then 11 after being on a charger. 12-13volts.

To be clear I was talking about the output of the alternator it self.
 

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Discussion Starter #10
Your battery should be reading more then 11 after being on a charger. 12-13volts.

To be clear I was talking about the output of the alternator it self.
I haven't had a chance to test the alternator itself, it started raining shortly after I got to test the battery. I also started multiple times after cleaning the connections to the alternator so I'd expect this type of voltage from not charging.

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1998 ML320 (W163)
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Discussion Starter #11
Was that the case with old alternator?
Battery light was not on with old alternator, as I said in the original post, the only reason I got the new one was because mine was noticeably not charging upon initial start, however during driving it would begin charging.

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Battery light was not on with old alternator, as I said in the original post, the only reason I got the new one was because mine was noticeably not charging upon initial start, however during driving it would begin charging.

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Old alternator had some residual magnetism that's why it would self exite at higher rpm. New one has none.
Start simple, remove cluster and replace bulb for charging light. Any LED mods done to the cluster?
 

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you should read about...

12.45 volts on battery charged car not running.
14.45 volts on battery after start.

To solve any mystery as to a bad new alternator pull it out and have it benched
tested. I don't know if you brought it local or internet but many shops will test it.
 

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Don't remove alternator. Use test light. Connect alligator to B+ (big lug) other end to D+ (small lug) start engine, check charging voltage.
 

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Don't remove alternator. Use test light. Connect alligator to B+ (big lug) other end to D+ (small lug) start engine, check charging voltage.
I agree with you as well, post #4.

Just giving another option to verify.

Because until it is known if the alternator is even putting out voltage we are chasing our tails.
 

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1998 ML320 (W163)
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Discussion Starter #16
Don't remove alternator. Use test light. Connect alligator to B+ (big lug) other end to D+ (small lug) start engine, check charging voltage.
Will try when I get home tonight. I don't have any alligator clips, all I have is a multimeter, which post would be positive and which negative? I'd assume the larger is positive and smaller is negative??

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Discussion Starter #17
Did a little further testing this morning, I'm getting battery voltage on the big lug, however I'm getting no voltage on the little one, I did look at a wiring diagram of the charging system from Mitchell1 and checked fuse 22 in the fuse box accordingly, fuse 22 was fine. Any other suggestions?
 

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1998 ML320 (W163)
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Discussion Starter #18
Upon, more further inspection, I had a bad connection in the wiring harness itself (some jackass screwed the wiring up before I owned the car), fixed the connection, now I have a battery light and 14 volts at the battery while it's running. Thank you all for your help, as per usual. I swear I could literally learn more about just my car everyday after over a year of ownership.
 
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