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Thread: 12v Alternator Issues

  1. #1

    12v Alternator Issues

    Okay, so the 55 Wagon has been 12v converted and now uses the alternator pictured below. The green wire connects to the box shown and the red wire attaches to the positive terminal on the fuse box, where the battery positive also connects. As far as I can tell, there is no voltage regulator (not external anyway).
    I have a Volt meter inside the cab, that when driving (2200 rpm or so) pins to like 18v. Also my headlight brightness is affected by my engine RPM.

    So, something is not kosher for sure. I recently had the headlights keep popping a fuse and am working on replacing everything in the headlight circut (wires, switches, fuse box ect) and I suspect that too high voltage may have caused some of the issue.

    What should I do? I have come up with a few options, not sure which is best or even viable.

    1. Could just replace the alternator (expensive)
    2. Could run the Alt output to the battery and then just the battery to the fuse box. Using the battery as a way to regulate the voltage, but I'd wonder if putting 18 volt to the battery will damage it.
    3. I could add a voltage regulator into the circuit somewhere. This should work but if the Alt is supposed to have one that isn't working would this just be a band-aid for bigger issues?

    What have I missed??

    Thanks all!

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  2. #2
    Senior Member
    Join Date
    Jan 2015
    E OK
    Hooking the alternator direct to the battery would change nothing since they are already connected through the fuse block.

    Fuses are amp sensitive. A few extra volts wonít hurt them. A short or bad (corroded) connection will draw the amps required to blow a fuse.

    18 volts to a 12 volt battery will hurt the battery if done for very long.

    I donít know enough about alternators to know if yours has an internal regulator but it sounds like you need a regulator.

    Edit: That black box looks like a regulator to me.
    '51 CJ3A
    '47 CJ2A

  3. #3
    Super Moderator bmorgil's Avatar
    Join Date
    Dec 2018
    Northwestern Ohio
    We need LarrBeard to hop in here. It sounds like you are full fielding the alternator. In other words, it is putting out full voltage all the time. As RPM increases the alternator just keeps putting out more. I think Jeff is on to it, something is up with the regulator.
    Last edited by bmorgil; 11-05-2022 at 02:56 PM.

  4. #4
    Super Moderator LarrBeard's Avatar
    Join Date
    Nov 2014
    Ft. Wayne, IN
    I’m always a bit leery about 12-volt conversions because you never know just who did what with wiring.

    A. You comment you have 18-volts on your voltmeter. That’s wayyyyyy too high - you are going to boil a battery and destroy it.

    B. Do you have an ammeter in the charging circuit? If you do, it is probably reading a LOT of charge current at an 18-volt system voltage.

    C. You also mention that lights change with engine speed. That indicates an unregulated condition.

    So - I am going to assume that you do not have an alternator problem - it is making a LOT of power - it just isn’t being regulated properly.

    I believe you have a “two-wire” alternator. The big wire is, of course, the wire that provides charging current to the battery. The smaller wire on the alternator (the push on terminal) is the terminal that provides DC exciting current to the field coils of the alternator.

    As a test, just disconnect that terminal from the alternator. The system voltage should drop radically. The alternator may still charge some from residual magnetism in the field coils, but probably not much if any.

    If that happens, a replacement regulator is in order. You are looking for something like this.

    It doesn’t look the same, but it does the same. The IGN wire goes to the existing IGN and the FLD goes to the FLD. Easy-peasy......

    …… Unless someone has hooked up something really weird - in which case life will be interesting. I would suggest that you include an ammeter in the circuit somewhere - if not the original one, another one externally. Voltage is nice, but what counts is current into and out of the battery.

    Let us know what you find out …..
    Last edited by LarrBeard; 11-05-2022 at 02:31 PM.

  5. #5

    You were very correct, I disconnected the Fld wire and it stopped charging. After some searching I was able to find an exact replacement for the regulator that I had in there (I like being able to keep the classic look)

    In case anyone needs one in the future and stumbles on this thread it was a "2VR9" and was cheaper at O'Rilley then at NAPA by like $20 (otherwise I would have gone to Napa, I can't stand my local O'Rilleys employees)

    Installed it today and the Volt meter goes to 14 and stays there!

    Thanks again,


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