gen light on when car is off

Discussion in 'Electrical Systems' started by ChevyPete, Sep 22, 2020.

  1. ChevyPete

    ChevyPete New Member

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    hey guys haven't been on here in a super long time but my 76 is having an issue it just started tonight I took my lady to the pizza shop about a mile down the road then go tear the town when we arrived the gen light stayed on.. it has never done this before the only thing electrically relevant that has been messed with recently is the choke on the carb I had rebuilt about 5 days ago but i have been driving it a couple times before now and not had an issue. At this point I'm thinking alternator or regulator when i unplug the two prong wire on the alternator it goes off..plug it in it goes on this is all with the car off when i switch the key on the oil light comes on and gen goes off. so far the alt looks like the smoking gun but how can i be sure its not regulator? anyone have a picture with the location of it? I'm not quite sure what I'm looking for. I know alts have internal regulators is there a way to detect if mine is the case? I'm not too familiar with electrical on vehicles but if i can fix it as appose to bringing it in id like to try. if needed i can post a video also. any help is appreciated and thanks in advance
     
  2. McCune

    McCune Veteran Member

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    The rectifier (diodes) is blown in the alt. Replace it.
     
    BillyDean7173 likes this.
  3. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    You can Google the test procedure.
    But if you don't have a good place to get alternator parts and don't have a multi-meter to test it.

    A parts store replacement for a stock alternator isn't very expensive and is very easy to replace.
     
  4. ChevyPete

    ChevyPete New Member

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    i did a quick search and to my understanding to test the diodes in the alt. with a multimeter on diode if you place negative on the positive post you'll get a reading. when you flip it and still get a reading then the diodes are bad. i went to try this about 5 minutes ago the alt. seems fine with polarites reversed i was getting .534 then switched them and got zip. where should i go from here ?
     
  5. ChevyPete

    ChevyPete New Member

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    So i called around today and found an alt as a hailmary you were right sorry for doubting slapped that sucker in and problem solved! I still wonder why the test didn't quite work with my old one though to see if diodes were bad
     
  6. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    Were you testing the diodes in the rectifier?
    [​IMG]
    Or the diode trio?
    [​IMG]

    Either way.... Glad you got it working again!
     
  7. McCune

    McCune Veteran Member

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    Probably because the unit was still together.
     
  8. patroll

    patroll Veteran Member

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    Sounds like a bad internal regulator gone bad they usually drain the battery while sitting, bad diodes in the alternator, loose fan belt will cause it ,I had to put a backup bolt to keep my belt tight a loose belt will cause a interment light to come on and off . Take it to a parts store they will check them out for free usually . Good Luck
     

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