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Thread: 2000 750il Battery indicator light

  1. #1
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    2000 750il Battery indicator light

    2000 750il battery light.
    Issue.
    Top battery is at about 90%
    Bottom battery is at about 80%

    My sons truck got stuck so I gave him a jump from the Top battery.
    Now...my battery light is on and when I run the system voltage check, its at about 10.8~11.00. Wont go past that.
    Did I F something up on my car?

  2. #2
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    Unfortunately you have damaged the regulator on the alternator, or the battery isolation switch that connects the two batteries under control of the DME. If it is the alternator regulator - this can be replaced as a separate unit rather than replacing the complete alternator.

    http://www.meeknet.co.uk/e38/Alternator/Index.htm

    For V8 - but V12 similar:

    http://www.meeknet.co.uk/e38/Alterna...eplacement.htm

    If it is the battery isolation switch there's more information here:

    http://www.meeknet.co.uk/e38/E38_Dua...ery_System.pdf

    Reading your post again I would guess that the switch is the problem as jumping from the top battery would have demanded excessive current from the switch.....
    Last edited by Timm; 01-13-2018 at 06:46 PM.
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  3. #3
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    Timm is right. There are rebuild kits for the water cooled alternators, but a rebuilt alternator is a better choice - beware that the 750 gets a different part from the v8. If you jump, I think you should do it from the under hood terminals, not the battery terminals. I don’t know if that caused your alternator to fail.

  4. #4
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    Quote Originally Posted by CPHES View Post
    ... If you jump, I think you should do it from the under hood terminals, not the battery terminals. I don’t know if that caused your alternator to fail.
    Ditto...if at all possible...always jump and be jumped using the jump start teminals in the engine bay:

    {see last paragraph in far right column}



    {V12 engine bay jump start terminals}

    (if my grammar, spelling, or sentence structure is screwed up....don't blame me...it's my dang bluetooth keyboard...I try to catch & correct the mistakes...but I may not catch all of them.)

    Q {BMW CCA Member #191509}
    2013 650ix GC (Black Sapphire) 1/13 mfg date <<~>> 2006 X5 4.4i (Sterling Gray) 12/05 mfg date
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  5. #5
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    Has anyone ever rebuilt a watercoolded Alt??

  6. #6
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    Look at Timm’s site. The meeknet links are excellent. Yes, it can be done, and there are kits, but you need to know what you are doing. Are you skilled that way - not to be harsh, but learning to do this on a 750 is a bad idea.

  7. #7
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    Quote Originally Posted by Magus528 View Post
    Has anyone ever rebuilt a watercoolded Alt??
    You can use one from the M62TU which is dime a dozen in junkyards, reuse the 750's pulley if it's different (some cars might still be equipped with the 49mm pulley).
    Last edited by XAlt; 01-15-2018 at 05:22 PM.

  8. #8
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    If I went into the "hidden menu" and went to test 9...and the voltage is only 10.8~11.00 when running...then is sounds like it would be the alternator an not the battery isolation switch correct?

    I feel pretty comfortable getting the alternator out and rebuilding it if necessary...but the link only gives information about the isolation switch...not how to repair it.

    Also...If anyone knows Max Lumens....tell him to get at me...I need some info. Thanks
    Last edited by Magus528; 01-16-2018 at 05:00 PM.

  9. #9
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    Yes, the battery indication light does mean the alternator is at fault - the signal for the warning light comes from the alternator itself - but make sure it is actually turning first!
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


    My Current 840ci Sport Individual
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  10. #10
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    Quote Originally Posted by Magus528 View Post
    If I went into the "hidden menu" and went to test 9...and the voltage is only 10.8~11.00 when running...then is sounds like it would be the alternator an not the battery isolation switch correct?

    I feel pretty comfortable getting the alternator out and rebuilding it if necessary...but the link only gives information about the isolation switch...not how to repair it.

    Also...If anyone knows Max Lumens....tell him to get at me...I need some info. Thanks
    Spare yourself the time of rebuilding it, water cooled alternators for the TU are everywhere.

  11. #11
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    Timm’s Page is great. There are many links on it. His links above in this thread should cover most of what you need. From above http://www.meeknet.co.uk/e38/Alternator/Index.htm

  12. #12
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    Quote Originally Posted by XAlt View Post
    Spare yourself the time of rebuilding it, water cooled alternators for the TU are everywhere.
    Lowest price I have seen is about $250-$275.

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