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Thread: HELP new alternator new battery, still wont charge 89' 325is

  1. #1
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    Exclamation HELP new alternator new battery, still wont charge 89' 325is

    So I recently got done swapping in a 2.7 stroker into my 89' 325is after I threw a rod and the car runs perfect but the battery wont charge I've replaced the battery alternator and ground wire going from oil pan to engine bay and when I test the voltage at the fire wall I'm getting nothing so I know the problem is in the engine bay just can't figure out what.

  2. #2
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    check the voltage for the exciter wire on the alternator. If you are not getting voltage from there, the alternator wont start unless you rev the engine. Also, i think there are a couple of ground wires that need to be connected.
    1987 BMW 325i Convertible


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  3. #3
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    Do you have 12 volts at the back of the alternator? On my 85 there is a power cable that goes from the starter to the alternator...is that connected?
    2004 525i Sport, Manual - 1985 325E Coupe Manual

  4. #4
    richardodn's Avatar
    richardodn is offline Old Guy BMW CCA Member
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    The alternator has 3 connections.
    1. Exciter wire (D+) that tells the alternator to start charging. This is the lighter gauge wire and voltage comes through the alternator light in your cluster. Does your alternator light turn on when you put the ignition on but not started? If it does this connection should be good. If not, then it's possible the exciter isn't telling your alternator to start charging. Most later clusters have a bypass resistor that will still allow voltage to the exciter even if the bulb is burnt out. If the bulb is out, disconnect the exciter wire and check for voltage. Reconnect when finished.
    2. Charge wire (B+) that carries the charge current. This is the heavier gauge wire and goes from your alternator to the main post on your starter. That's the same one as the thick cable from your battery. Assuming the alternator is charging, the voltage on the back of the alternator should be 13-14.5 volts. If you have voltage from the alt but not at the battery, the problem is in between.
    3. Ground goes through the alternator case, brackets, engine block, ground strap, chassis, (-) battery cable to the battery. If you have the earlier style alternator with the rubber isolation mounting bushings you would have an additional ground strap from the alt to the brackets/engine. Make sure the connections are all clean and tight. I had a weird charging/starting issue once due to the (-) cable connection to the chassis being loose.

    So basically check to see the disconnected exciter is getting voltage with the ignition on. If it is, reconnect it, start the car and check charge voltage off the alternator and at the battery. That will narrow down where your issue is. If you go through all this, be sure to report what voltages you are seeing.
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  5. #5
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    thats correct and I just replaced mine still not charging the battery

  6. #6
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    starting with battery voltage of 12.5, yes alternator light the one that looks like a battery with pos and neg stays on when car is off and running.

    tested the voltage at the alternator posts when running 1.5v this is after just replacing the B+ wire with a 6 gauge wire

    the only things i have connected to the alternator are the pos that goes to starter, the exciter blue wire and the alternator adjustment bracket that I removed all paint from the metal on metal areas

    besides the ground from oil pan to chassis are there any other ground that connect to engine I didnt touch any of the other grounds that were only in the engine bay during the swap

    I painted the alt bracket and block with black heat resistant paint, currently removing the paint on the bracket and where it touches the block to see if thats were my grounding problems is

  7. #7
    richardodn's Avatar
    richardodn is offline Old Guy BMW CCA Member
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    The main ground strap down below is the only one you need for starting/charging. There's actually a second ground strap between the firewall and valve cover but that's just for radio noise suppression.

    You can do a simple continuity check by measuring resistance (ohms) between the alternator case and the chassis. It should be near 0 ohms.
    "Howdy, Folks!"

    1986 Delphin 528e - Roof rack equipped lumber hauler.
    1989 Zinnoberrot 325iX Sedan - I miss this car. (Deceased)
    1998 Avus Blau 328iC - Someone else's project now
    2008 Platinum-Beige X3 3.0si - Current project
    2012 Alpine White X3 xDrive35i - My new snowmobile.
    2020 Estoril Blue 440i xDrive cabrio - This car is a blast to drive.

  8. #8
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    Quote Originally Posted by tomstin View Post
    Do you have 12 volts at the back of the alternator? On my 85 there is a power cable that goes from the starter to the alternator...is that connected?
    yes I replaced it with a new one

  9. #9
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    Im stumped I had alt tested and its good, I removed paint from block and alt bracket, the B+ wire is new, exciter wire should be okay if alt light is on when car is off, and the main ground for charging is new.

    only thing i can think is theres another ground issue, don't know if this would make a difference but PO put a 12in sub in the back wiring looks pretty clean and my ABS, parking break light are now on after the swap

    going to keep following wire and see if i see any suspect if I don't itl'l be going to a shop next week. thanks for all yalls help

  10. #10
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    No e30s, again :(
    the sub shouldn't cause any trouble. I think a lot of us have added subs and stereo stuff to our cars in the past. I know I had two 12s back in the day and my youngest son has three 10s in his.
    No e30s again.

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