Need help...dual field alternator

Electrical & Ignition

  1. dsd1967

    dsd1967 Well-Known Member

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    I bought a 67 D100 pickup less motor and trans. The previous owner had converted it to a dual field alternator system. I hooked up the dual field alternator and it acts like it's not charging at all. I rev the motor and the needle on the dash and the aftermarket gauge both stay rock solid at 12 volts. I turn the lights on and it drops very slightly and revving the motor doesn't do anything. The needle never moves....not even back to 12 volts.

    I've tried a different VR and it acts the same. Is this normal operation for a dual field system?

    I know the alternator puts out a charge because I originally put a single field alternator in it and hooked up the blue wire by mistake...and it would put out 17 volts unregulated.
     
  2. Shorthorse

    Shorthorse Well-Known Member

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    Regulators ground via the screws into the firewall. Make sure your new regulator is well grounded. New ones can have a pretty thick coat of paint on them.
     
  3. dsd1967

    dsd1967 Well-Known Member

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    It's a plated solid state VR and there are two bolts with those star washers securing it. I'll run a continuity check to make sure it's grounded just to be sure.

    I also messaged the previous owner to see if it acted like this for him.

    I'm half tempted to make it a single wire system and get an old style VR just to see if it works
     
  4. pnora

    pnora FBBO Gold Member FBBO Gold Member

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    It is a simple system. Make sure you have battery voltage at the alternator stud. Then turn the key on you should have voltage on the blue wire. Unplug the green at the alternator. Start the engine and ground the terminal on the alternator that you removed the green wire from. It should full field and charge like crazy. If not while the ground is still attached verify battery power at the stud and blue wire. If they both have battery power it is the alternator thats bad. I can diagnose these old systems in a minute with a volt meter and jumper wires.
     
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