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  1. #1
    Bronze Member
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    ford 420 industrial with custom turbo setup, diesel converted wheel horse

    Default externally regulated alternator question

    I have a 75 ford 420 industrial (i think). It appears to have the factory alternator with external regulator. It hasnt charged since I've owned it. I put a new aftermarket regulator in it first, but no change, charge light stays lit and voltmeter says no charge at all. I did some research on these alternators and found some pictures that show what each post is. I did figure out how to 'full field' it and it charged very well then (15-16 volts) and the charge light went out for the first time ever! Sounds like a bad regulator, except mine is new. Now maybe I got a bad Chinese made regulator (certainly possible), but I would like to trouble shoot a bit more before I drop some more money on another regulator.

    Here is the ugly old girl that I am working with

    the green wire with brown stripe that is just hanging with a ring terminal was just hanging with no connector. I added the ring terminal and put it on the lowest post (4:00) position because i thought maybe there is a stray wire and an empty post, they go together? This made no change so i removed it. That stray wire is not grounded and has no voltage on it. Dont know what it is. The feild (top, 12:00) terminal has about 2.5 volts with engine not running (key on) and about 10.5 when running. The regulator terminal (9:00) has about the same voltage as the field terminal under key on not running and running. I already rewired the ignition switch on this which was all sorts of backwards, and I think i have that right, everything else now behaves like it should. I dont assume the alternator is wired correctly, Im just not sure how to tell.

    Looking for some pointers where to go from here, not sure how the regulator is supposed to behave. My old one looked like it got hot and melted all of its insulation out at some point. This new one has never gotten hot, but it also never worked with it. I am happy to find that alternator works, if I could just get the rest of the system working my tractor would be happy and I could install some lights and run them!

  2. #2
    Super Member RickB's Avatar
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    Case 885, Ford 4000

    Default Re: externally regulated alternator question

    The photos of your nice turbo installation in the other thread show a new VR hanging by its wires and the old one firmly mounted in place. First thing I'd do is mount the new VR making sure the mounts are clean & bright and see if it does its job when properly grounded.

    Edit: A faulty charge indicator lamp bulb or corroded lamp socket might keep the charging system from being properly excited. There is also an inline fuse behind the instrument cluster that protects the charging system.
    We have too much gun control.
    What we need is more idiot control.

  3. #3
    Bronze Member
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    ford 420 industrial with custom turbo setup, diesel converted wheel horse

    Default Re: externally regulated alternator question

    Quote Originally Posted by RickB View Post
    The photos of your nice turbo installation in the other thread show a new VR hanging by its wires and the old one firmly mounted in place. First thing I'd do is mount the new VR making sure the mounts are clean & bright and see if it does its job when properly grounded.

    Edit: A faulty charge indicator lamp bulb or corroded lamp socket might keep the charging system from being properly excited. There is also an inline fuse behind the instrument cluster that protects the charging system.
    I actually mounted it right after i completed the turbo installation, appears to be well grounded.
    I did some more probing using some more info i got on the internet. According to the guide i found, the red wire should be constant 12v, the yellow should be switched 12v. Both my red and my yellow are switched 12v. I got brave and cut the red wire at the regulator and jumped 12v straight to it. Low and behold it charged at just about 14v across the rev range. I did measure the amps from battery to red wire with all other things off and it was drawing 2.3a. I think this would leave my battery dead quite quickly if i wired it permanently like this. I did replace the old malfunctioning ignition switch with a universal one from napa. It just has a 12v in, switched 12v and starter post. Maybe this is the root of my problem. When I jumpered power to the red wire it charged well but the light no longer functioned (stayed off even when I killed the engine with key on)
    I think my confusion at this point is because I really dont understand what needs to happen to make this regulator work and the lamp work also. Maybe i need to find another switch that has a stand alone post for the charging circuit.

  4. #4
    Platinum Member Qapla's Avatar
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    New Holland TC40D HST 4WD FEL/BH

    Default Re: externally regulated alternator question

    On many vehicles that have external regulators you need to "polarize" the regulator before it will work. Not sure if this applies to your situation.
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  5. #5
    Bronze Member
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    ford 420 industrial with custom turbo setup, diesel converted wheel horse

    Default Re: externally regulated alternator question

    Quote Originally Posted by Qapla View Post
    On many vehicles that have external regulators you need to "polarize" the regulator before it will work. Not sure if this applies to your situation.
    i think that process polarizes a generator but not needed for alternator. Not really sure though. I have never messed with an externally regulated alt before. I'm all ears.

  6. #6
    Gold Member
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    loganville ga
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    wheel horse c-100

    Default Re: externally regulated alternator question

    you need not polarize regulator but these units are notorious for doing exactly what you are describing may need to take alternator and regulator to local rebuilder where they can put it on test stand and check all functions these units will run you in circles trying to fix if you cant locate rebuilder repost and i will find you one in your area

  7. #7
    Platinum Member sd455dan's Avatar
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    Ford 3000-Rhino 554,Co-Op ,Honda ,Gilson riding mowers

    Default Re: externally regulated alternator question

    Quote Originally Posted by VTPSD View Post
    I have a 75 ford 420 industrial (i think). It appears to have the factory alternator with external regulator. It hasnt charged since I've owned it. I put a new aftermarket regulator in it first, but no change, charge light stays lit and voltmeter says no charge at all. I did some research on these alternators and found some pictures that show what each post is. I did figure out how to 'full field' it and it charged very well then (15-16 volts) and the charge light went out for the first time ever! Sounds like a bad regulator, except mine is new. Now maybe I got a bad Chinese made regulator (certainly possible), but I would like to trouble shoot a bit more before I drop some more money on another regulator.

    Here is the ugly old girl that I am working with

    the green wire with brown stripe that is just hanging with a ring terminal was just hanging with no connector. I added the ring terminal and put it on the lowest post (4:00) position because i thought maybe there is a stray wire and an empty post, they go together? This made no change so i removed it. That stray wire is not grounded and has no voltage on it. Dont know what it is. The feild (top, 12:00) terminal has about 2.5 volts with engine not running (key on) and about 10.5 when running. The regulator terminal (9:00) has about the same voltage as the field terminal under key on not running and running. I already rewired the ignition switch on this which was all sorts of backwards, and I think i have that right, everything else now behaves like it should. I dont assume the alternator is wired correctly, Im just not sure how to tell.

    Looking for some pointers where to go from here, not sure how the regulator is supposed to behave. My old one looked like it got hot and melted all of its insulation out at some point. This new one has never gotten hot, but it also never worked with it. I am happy to find that alternator works, if I could just get the rest of the system working my tractor would be happy and I could install some lights and run them!

    Not totally sure -but that appears to be a Motorola alternator. the top wire in your picture is the field wire (usually green or green white and is + brush wire) the one on the left side of the picture should be the aux or regulator wire (orange or red from the regulator), this terminal also connected to the charge light . The bottom connection is the main battery + . The two posts on the right of the alt are grounds one to battery(not always used) - and one to the regulator ground. The basic theory and tests will work from late 1960s Jeeps and also AMC cars and trucks of the same vintage up to about 1974 that used the Motorola set up and of course also Ford

    I had similar problems with the wifes AMX - low to no charge especially at idle and after replacing both the alt and regulator - everything worked, Charged at 14.2 volts but the charging system would drain the battery over night . Got fed up and installed a relay in the regulator wire (between the regulator and the left 9 oclock terminal in your picture that only gets connected to the regulator when the key is on ... Everything works great now. Starting to think there is something up with the new regulators or remannufactured alternators isolation diodes... Hope this helps
    Last edited by sd455dan; 08-27-2013 at 04:08 AM.

  8. #8
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    ford 420 industrial with custom turbo setup, diesel converted wheel horse

    Default Re: externally regulated alternator question

    Quote Originally Posted by sd455dan View Post

    I had similar problems with the wifes AMX - low to no charge especially at idle and after replacing both the alt and regulator - everything worked, Charged at 14.2 volts but the charging system would drain the battery over night . Got fed up and installed a relay in the regulator wire (between the regulator and the left 9 oclock terminal in your picture that only gets connected to the regulator when the key is on ... Everything works great now. Starting to think there is something up with the new regulators or remannufactured alternators isolation diodes... Hope this helps
    that is exactly what I was thinking of doing if i cant figure out what it behaves like that. Mine seemed to work just like it should with straight battery power to the red regulator wire, just that 2.3a draw would certainly kill my battery overnight. The only downside for doing that would be that my charge light does not appear to operate when wired this way......Probably would have been better off converting to a cheap internally regulated alternator from the start.

  9. #9
    Super Member RickB's Avatar
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    Default Re: externally regulated alternator question

    These systems are reliable when everything is correct. You have an ignition switch that doesn't have the proper configuration, a 35 year old harness and indicator lamp sockets, and a generation worth of corrosion on the connectors. Maybe a wiring diagram, a decent ignition switch and some maintenance are in order.
    We have too much gun control.
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  10. #10
    Bronze Member
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    ford 420 industrial with custom turbo setup, diesel converted wheel horse

    Default Re: externally regulated alternator question

    if i had a diagram of how it was supposed to be, i would be set. Not the easiest thing to come by, particularly when I am not even 100% sure of what tractor I have.

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