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  #1  
Old 04-01-2013, 02:22 PM
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What is this little Alternator part? On Bosch AL-117x.

I've been having trouble with my alternator on my 78 300d. I replaced the voltage regulator but that didn't help. So I decided to get a new one and upgrade to the al117x since it was the easiest upgrade to do.

The real problem here might be some faulty wiring placing an extra draw on my battery, but I had already ordered this so I'm going to give it a shot.

Anyways, I've attached a pic of both alternators. The new one is missing a little piece that plugs into the positive terminal - can I just use the one from the old alternator? Does it matter that they aren't the same model? Or could this little thing be the problem?

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What is this little Alternator part? On Bosch AL-117x.-photo-2.jpg   What is this little Alternator part? On Bosch AL-117x.-photo-1.jpg  
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Old 04-01-2013, 02:27 PM
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The "little piece" is a capacitor for noise suppression. Did you have the old alternator tested or do any voltage checks of your own, before replacement?
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  #3  
Old 04-01-2013, 02:38 PM
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Yes, it was in the 13's for the most part when I tested it. Someone here suggested a parasitic load draining power when the car is off. I had already ordered this part so I figured I'd put it in first. Also, diagnosing a parasitic load sounds like looking for a needle in a haystack
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Old 04-01-2013, 02:57 PM
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Quote:
Originally Posted by SD Blue View Post
The "little piece" is a capacitor for noise suppression.
X2.

Some MB alternators came with it and others not. My understanding is its supposed to keep the radio from picking up static from the drivetrain.
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Old 04-01-2013, 04:41 PM
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alternator is in. it's at 14.10 at idle. i guess that's ok? i don't know whether or not to unplug this battery overnight or risk it.
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Old 04-01-2013, 06:22 PM
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To see if there is a draw when the car is off, I unhooked the negative battery cable and measured with a multimeter between the negative terminal of the battery and the cable. I'm not sure if I'm using the multimeter correctly but when it is set to 200A, I get a reading jumping around between 65-75.
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Old 04-01-2013, 06:40 PM
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... I doubt you have a 200A multimeter... they are pricey. you could have a 200A indirect meter, does it have a clamp on it? more likely you have 200mA setting. 65-75mA would be totally acceptable draw.
take a picture of the dial on the meter and post it here.
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Old 04-01-2013, 08:17 PM
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here's a pic of the meter. thanks.
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What is this little Alternator part? On Bosch AL-117x.-multi.jpg  
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Old 04-01-2013, 08:21 PM
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yes, now that i think about it, i meant milliamps, not amps!
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Old 04-01-2013, 08:22 PM
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i've been through a lot with the battery and alternator, so i'm paranoid about this now. i think i'm going to unhook my bsttery every night.
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Old 04-01-2013, 10:17 PM
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Bingo!

Quote:
Originally Posted by Walkenvol View Post
X2.

Some MB alternators came with it and others not. My understanding is its supposed to keep the radio from picking up static from the drivetrain.
Walkenvol is totally correct. That capacitor is totally optional from a reliability standpoint. It is very unlikely to be your parasitic drain, but if you are worried about it, just remove it. Perhaps more static on the radio, but no other problems will result.

There are aftermarket battery terminal switches that you can install to disconnect the battery easily each night, if you cannot find your parasitic load. Good luck.

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