Battery not charging with new alternator?

Discussion in 'Troubleshooting & Diagnosis' started by Andelin74, Feb 14, 2011.

  1. Andelin74

    Andelin74 Veteran Member

    205
    0
    Oct 28, 2010
    Bakersfield, CA
    Ok so here's the story: My battery has been dying a bunch these past few weeks, so i tested the alternator and it wasn't giving a charge, I assumed the alternator was bad and put a brand new one on.

    Now i hooked up the voltage tester to the battery with the new alternator and the car still seems to be running off just the battery (at about 12 volts). So, like anyone else, i assumed it was an issue with wiring, maybe an old wire had stopped working or something, so to make sure I ran a wire straight from the BAT terminal on the alternator to the positive battery post.

    STILL no charging, does this mean it's an issue with the battery? I've been charging it with an external charger without any problems at all, so i don't see why it wouldn't take a charge from an alternator, any help would be awesome.
     
  2. Kamikaze

    Kamikaze Veteran Member Lifetime Gold Member

    Need to charge up your battery first then do a load test on it to verify it's condition is still good and will accept a charge.

    If it has dead cells, and won't accept a charge, you may have already had a good working alternator but also a bad battery
     
  3. Bikefixr

    Bikefixr Veteran Member Lifetime Gold Member

    1,560
    0
    Mar 13, 2006
    Is it a single-wire type alternator? If so, you have to excite the Diodes by revving to about 2000 RPM. If it's astock type, then you need to make sure the alternator actully turns on. The big red wire goes to the starter and eventually tot he battery. The plug that sticks intot he alt case has 2 wires in it. One of them is keyed 12v and that tells the alternator to turn on. If you have a bad plug, or broken wire, the alt will spin but do nothing.
     
  4. crome dome

    crome dome Veteran Member

    525
    0
    Oct 27, 2008
    Round rock Texas
    Wasn't there also a topic awhile back about not having the charging dummy light in the instrument panel and that could cause the alternator to not turn on. Seems I remember this being a problem for some folks after they installed aftermarket guages.
     
  5. Cardinal

    Cardinal Veteran Member Lifetime Gold Member

    8,166
    0
    Jun 22, 2003
    Endicott, NY
    +1 for "alternator idiot lamp" burned out. I had a 80 Monza 2+2 that drove me nuts when the alternator wouldn't charge! Finally a friend of mine told me to change the alternator idiot light. Alternator started charging.
     
  6. Andelin74

    Andelin74 Veteran Member

    205
    0
    Oct 28, 2010
    Bakersfield, CA

    You just triggered a light bulb. I actually just removed the stock instrument cluster completely from the harness about 2 months ago. And i did notice that the alternator was only using 1 wire from the harness slot, and that one was being jumped to the BAT terminal. So technically, I could just run a wire from the other post on that harness(the one that is meant to go to an indicator) to any accessory "key" wire and it should start the alternator up right?
     
  7. Fbird

    Fbird Veteran Member Lifetime Gold Member

    2,094
    10
    Feb 12, 2011
    atlanta, ga
    yup. here is the simplist diagram i have (hope it posts)
    Alt%20wiring.jpg
     
  8. mrvedit

    mrvedit Veteran Member

    1,346
    1
    Jun 12, 2009
    Ann Arbor, MI
    IIRC the "activate" line to the alternator needs to go through the idiot light or a resistor (around 100-400 ohms) or the alternator, depending on the model, might burn out.
     
  9. Andelin74

    Andelin74 Veteran Member

    205
    0
    Oct 28, 2010
    Bakersfield, CA
    Thanks guys, installed a new dummy light wired to a keyed wire and it fired right up!
     
  10. crome dome

    crome dome Veteran Member

    525
    0
    Oct 27, 2008
    Round rock Texas
    Good job. Does your car still have the factory guages. I still have to figure out where to add a bulb or resistor since I removed all the factory guages and lamps.
     

Share This Page