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my battery is not keeping a charge all the time. most of the time after you shut off the car it will need a jump to start it again. but not ALL of the time. 2 mechanics have said that the alternator is good one has said it was bad. the battery does not ever lose power while i'm driving it, only when i turn it off . and for the first time the other day the battery light did come on while i was driving it. could it really be the alternator or could it be something else like a short in the electrical system somewhere? no one can seem to figure it out. does anyone out there have any theories. help!
 

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123gigim said:
my battery is not keeping a charge all the time. most of the time after you shut off the car it will need a jump to start it again. but not ALL of the time. 2 mechanics have said that the alternator is good one has said it was bad. the battery does not ever lose power while i'm driving it, only when i turn it off . and for the first time the other day the battery light did come on while i was driving it. could it really be the alternator or could it be something else like a short in the electrical system somewhere? no one can seem to figure it out. does anyone out there have any theories. help!
My W116 suffered this problem 2 years ago....till it killed the battery. Replace your voltage regulator, if all your connections at the battery and gounds look good. Mine would work fine 90% of the time. others it would drain the battery dead just sitting or overcharge. Assume nothing.
 

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Had similar issue. Very frustrating! Three different alternators later...

Definitely validate the voltage regulator first. But for my mysterious experience:

A good mechanic (third one I've been to on this issue) finally figured the thermo timer switch for the preglow is faulty and wired incorrectly, making the glow plugs stay on almost all the time. Someone rigged it at some point before I bought the car. Not good for the plugs, not good for the alternator or battery. Not good for my sanity either...but now I know what the problem is!

Now I'm trying to find this switch. The shop that found the problem hasn't gotten back to me for a week so I'm wondering if they're having problems finding it too. For the time being I'm disconnecting the circuit at the ground wire once the engine is started, and all is well.

Good luck with yours.
 
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