Charging issues

1975 - 1979 Mopars

  1. 78cordoba

    78cordoba Well-Known Member

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    Hey guys I'm having trouble getting more than 12.3 volts when the car is running and I'm at 12.6 with the car off. My alternator has been tested and was good. I'm not sure if it's a wiring issue or what's going on. Any help would be appreciated. Thanks all IMG_20200905_194538.jpg
     
  2. Builderguy

    Builderguy Builderguy FBBO Gold Member

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    On your 78 Cordoba, correct?
     
  3. 78cordoba

    78cordoba Well-Known Member

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    Yes that's correct IMG_20200902_171835.jpg IMG_20200822_213213.jpg IMG_20200822_213205.jpg IMG_20200801_141402.jpg
     
  4. Builderguy

    Builderguy Builderguy FBBO Gold Member

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    You already have my first suspect in your hand. If the alternator tested fine at the shop, then one of the first variables not at the shop and only on your car would be your voltage regulator. That is where I would start assuming you already did all the load tests with you car running (all accessories on, etc).
     
  5. 78cordoba

    78cordoba Well-Known Member

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    Is there a good way to test them also would a faulty ammeter cause a no charge situation? Just trying to rule everything out.
     
  6. Builderguy

    Builderguy Builderguy FBBO Gold Member

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    Quick question, your alternator, is that a REMY 20036? I ask because it only has one FLD stab with two wires going to it. I thought they are normally two separate FLD wire stabs.
     
  7. Builderguy

    Builderguy Builderguy FBBO Gold Member

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    I am pretty sure you car has a volt meter not an ammeter. Chrysler stopped using ammeters in 1975 if I remember correctly.
     
  8. 78cordoba

    78cordoba Well-Known Member

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    Yes it is
     
  9. 78cordoba

    78cordoba Well-Known Member

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    IMG_20200905_231817.jpg
     
  10. Builderguy

    Builderguy Builderguy FBBO Gold Member

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    Okay here is video of how to take the voltage regulator out of the loop. You really only need to watch it until about 2:30 after that he starts doing some things that we don't care about. If you get good alternator output then you can be pretty sure it is the regulator or the regulator ground to the firewall. That ground is very important and a layer of paint can easily mess that up. Here is the video: https://www.bing.com/videos/search?...1F6CCA2DCDD94277CE651&view=detail&FORM=VIREHT
     
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    • Builderguy

      Builderguy Builderguy FBBO Gold Member

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      I see that my memory is not that good anymore, maybe 1975 was when Mopar switched to a shunted unit. IDK But now you have me thinking about it so I will have to hit the history books to find the date they were dropped.
      Anyway a great source of information on the site when it comes to alternators or ammeters is Nacho-RT74. If he sees these posts he might chime in.
       
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      • 78cordoba

        78cordoba Well-Known Member

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      • 78cordoba

        78cordoba Well-Known Member

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        Ok green wire grounded on a ground wire to the block there is no change even if I raise the idle
         
      • 78cordoba

        78cordoba Well-Known Member

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        Also the smaller stud on my alternator is not hooked up to anything should it be grounded?
         
      • Builderguy

        Builderguy Builderguy FBBO Gold Member

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        Just so we are on the same page you grounded the green wire in the blue voltage regulator connector to a good ground. Increased the engine RPM but got no increase in voltage at the battery. Correct
         
      • 78cordoba

        78cordoba Well-Known Member

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        Yes that's correct
         
      • Builderguy

        Builderguy Builderguy FBBO Gold Member

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        Okay, I don't want to give you bad information, and I don't know this alternator that well, so give me a minute to look something up.
         
      • Builderguy

        Builderguy Builderguy FBBO Gold Member

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        Sorry about that. From what I found about your alternator, it should be case grounded so no ground wire to the little screw. Speaking of grounds, it looks like your alternator mounting brackets are brand new or at least have fresh paint on them. Being that the alternator is case grounded, this may cause a problem. You may want to run a dedicated ground wire to the alternator case just to make sure you have a good ground and then run the regulator green wire grounded test again to see if you get a jump in voltage with increased RPM.
         
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        • 78cordoba

          78cordoba Well-Known Member

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          Ok is the small stud a ground stud then could I just use that?
           
        • Builderguy

          Builderguy Builderguy FBBO Gold Member

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          Just so you know, there is not a lot of info on the web about this alternator and the wiring for it. I am not that familiar with this unit so I am only giving my experience info. You may want to go to the supplier and ask about the purpose for the small screw but if it was meant to be a ground for the case, it should have a ground symbol on it. That being said I really have no idea what the screw is actually for. The two fld stab units do not have this small stud.

          As for hooking up a ground to this small screw, IDK. I would not as I don't know the internal wiring and would not want to cause a short. I would attach the temp ground to the case where one of the mounting brackets bolts on that way your are safe and won't cause any damage to the alternator.
           
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