Can’t get an alternator to put out a charge

Electrical & Ignition

  1. detmatt

    detmatt Old Man with a Hat FCBO Gold Member

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    OK so I’ve been having a charging issue in my imperial for a while now and I’m trying to straighten it out. At this point it has me a bit baffled, The alternator that was in it I had tested and it failed so I bought a new one and installed it in hopes that this would solve this problem.
    With the battery fully charged I can’t get the alternator to put out over 12.2 volts.
    I get the same reading whether I am testing the output voltage at the battery or at the alternator and I have checked the resistance across all the grounds in between the battery the engine and the chassis. I also have taken the mechanical voltage regulator out of the equation with no change. I even went so far as to put the known good alternator from the Challenger in it and have the same result. I even swapped batteries and had no change in the situation. What am I missing here?
    Basically I can take the car with the battery fully charged and drive it over a period of several days and the battery slowly discharges to the point where it needs to be Recharged.
     
    Last edited: Jul 12, 2019
  2. Pete Kaczmarski

    Pete Kaczmarski Senior Member

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    First I would take the car and have it tested on the VAT. With a load I found my rebuilt Auto Zone alternator was putting out a third of its output. The second one was a little better but still half of under load output. It took a third one to get it right.
     
  3. furious70

    furious70 Active Member

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    What do you mean by you took the voltage regulator out of the equation?
     
  4. traintech55

    traintech55 Senior Member FCBO Gold Member

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    I take it that you are talking about your 64 or 67 Imperial. If you bypassed the regulator the alternator should have gone wide open to full charge when you grounded the green wire. Check the back of your new alternator and make sure they did not slip a new style alternator, (two wire clips) in the box. If they did you have to ground one of the clips, as your old alternator only had one wire.
    If all this checks out you probably got a bad one.
     
  5. detmatt

    detmatt Old Man with a Hat FCBO Gold Member

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    Basically trying to trick the alternator into thinking that it needs to be putting out a full charge.
     
  6. detmatt

    detmatt Old Man with a Hat FCBO Gold Member

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    They did give me one with the extra connector and I do have it grounded and I have the same result when I put the noon good alternator from the Challenger in the imperial. That is one of the square backed units which I also grounded it’s extra brush.
     
  7. 71NewYorkMan

    71NewYorkMan Member

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    Maybe a bad ground? Where do you have the ground connected? Have you tried grounding directly to the battery?
     
  8. detmatt

    detmatt Old Man with a Hat FCBO Gold Member

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    There is zero resistance between on the negative post of the battery and the case of the alternator.
     
    Last edited: Jul 12, 2019
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  9. traintech55

    traintech55 Senior Member FCBO Gold Member

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    Ok, next two things to check out, 1. Make sure the wire from the regulator to the alternator did not open up. 2. Make sure the new alternator has a good ground.
     
  10. detmatt

    detmatt Old Man with a Hat FCBO Gold Member

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    I’ve got zero resistance in the wire between the alternator and the voltage regulator and also no resistance between the ground and the alternator to the negative battery terminal. Since I have a dual field alternator I checked the resistance between both of those brushes in the battery and there was none. As far as the wiring on the new alternator I have the field connection plugged into the same connector that it was plugged into on the single field alternator and have the other one just grounded to the case of the alternator.
     
  11. traintech55

    traintech55 Senior Member FCBO Gold Member

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    Last thing to check before I am stumped, is the blue wire at the regulator hot with the key in the "Run" position?
     
  12. detmatt

    detmatt Old Man with a Hat FCBO Gold Member

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    Nope.
     
  13. 1978 NYB

    1978 NYB Warfighter FCBO Gold Member

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    Matt, I assume you bought the new alternator from AAP, AZ, or Napa or something like that.

    Did they bench test the the new one for you before you left the store? If not I would take it back. I know AAP has an accurate bench tester and it's almost idiot proof. I would bench test it before trying anything else. All of them have bad alternator or generators in the box occasionally.
     
  14. traintech55

    traintech55 Senior Member FCBO Gold Member

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    The blue wire to the regulator supplies voltage to turn the regulator on. It should be hot with the key in "Run" and "Start". If I remember right, there is a solder joint in the line, and it is the same line that feeds up to the ballast resistor.
    If it is not hot, then it cannot turn the alternator on, or off.
     
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  15. detmatt

    detmatt Old Man with a Hat FCBO Gold Member

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    For what it’s worth the new alternator came with a card saying that it was end of the line tested and it’s results.
     
  16. 1978 NYB

    1978 NYB Warfighter FCBO Gold Member

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    Doesn't mean it works....

    I would get it bench tested (free at AAP) and eliminate it as the problem.
     
  17. detmatt

    detmatt Old Man with a Hat FCBO Gold Member

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    I just checked that in the wire does not get warm. I have to run to a clients house real quick but I will be back on it in 45 minutes.
     
  18. detmatt

    detmatt Old Man with a Hat FCBO Gold Member

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    Don’t forget I took the known good alternator off of the Challenger and put it on the imperial this morning with the same results.
     
  19. traintech55

    traintech55 Senior Member FCBO Gold Member

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    When I said "Hot", I didn't mean to touch. It should have battery voltage on it with the key in the run position. Bet you have a break in the wire. I have to run to a doctors appointment, but if this is not it send me a PM with your number, and I will work with you over the phone when I get home. Bill
     
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  20. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    Try running a jumper from the battery lead on the alternator to the positive terminal on the battery and see if you get a charge then. If that does not work, try running a jumper from the field terminal to the battery. If it still does not charge, the alternator is toast. If you get a charge using the above methods, you have a wiring issue. Does the amp gauge move when the lights are turned on?

    Dave
     
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