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Alternator or voltage regulator

Discussion in 'The Garage' started by divorced, Nov 24, 2006.

  1. divorced

    divorced 3/4 ton status

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    Ok guys, It's not a Chevy but maybe someone can help....

    1976 F350 2wd with a 390.

    I tested the voltage at my battery and it's the same with the truck running or turned off. How can I tell if it is a bad alternator or just a bad voltage regulator?
    (It has an external regulator)







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  2. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    Sounds like the alternator.. Most voltage regulator failures I've seen allow too much voltage...
     
  3. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    the way i always test for a bad alternator is to start it and then remove a battery terminal. if it quits, the alternator is bad.

    it doesn't sound like a voltage regulator though, like ryoken said, they usually put out too much voltage.
     
  4. 3 on the tree

    3 on the tree 1/2 ton status

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    Does it have the solid state regulator, or the old points style? The points style, you can remove the cover, file the points and adjust them. I can't remember which ones, but there are two wires you can jump to make the alt go full chaarge, bypassing the reg.
     
  5. diesel4me

    diesel4me 1 ton status Premium Member

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    here's how..

    I would not try running the truck with the battery cable off to see if its charging--you can blow diodes doing that!...a safer crude test ,lacking a voltmeter, can be done with a screwdriver--hold it near the rear bearing in the altenator--if its charging,it will attract the screwdriver strongly to the case (while engine is running:rolleyes: ).....

    To test the regulator,unplug it,and either use a jumper tool designed for this purpose,or make your own jumper wire with solderless connectors that fit the harness you unplugged to the regulator...jump the terminals "A+" or "Batt" to the "F" or Field terminal together,(they are marked on the regulator where the harness plugs onto it) and run the motor slowly--if the alternator lamp goes out,or the voltmeter shows an increase in voltage,then the regulator is faulty,not the alternator...:crazy:

    On older Fords like this you can buy a solid state transistorized regulator,or a cheaper mechanical one..I prefer the solid state one,its sealed and cant get corrosion inside,a big feature here in the "salt-east"...:doah: ..We put a Delco 10SI alternator on our '70 F350 ramp truck with a 390 in it when the original motorcraft one croaked..didn't take much modification either!.:crazy:
     
  6. divorced

    divorced 3/4 ton status

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    It was a bad alternator. I replaced it and the regulator and all is well now. Thanks for the help!:waytogo:



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