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alternator works great but hums when ignition is off

Discussion in 'The Hokey Ass Message Board' started by 1950kale, Dec 24, 2013.

  1. 1950kale
    Joined: Jan 22, 2013
    Posts: 217

    1950kale

    hi everyone, does anybody know what is wrong with my charging system? i have a brand new alternator meant for a 1991 chevy silverado on my 1991 350 SBC, its in my 1953 chevy 3800, it charges great, battery reads 14.5 v when engine is running, but when the engine is off i can hear a faint electric hum coming from the front of the alternator. if i unplug the BAT of coarse it turns off but it wasent doing this untill i ran the Lamp wire to a power source on the fuse box, (i diddent have a idiot light, & it wasent charging unless i had power to this wire) there is too other wires that i read were not important, & were meant for the ECU when the engine was in the 91. does anybody know what is causing this? i am worried that the electricle leak will drain my battery if i leave it for a coupple days, and is this wire not ment to have that much power to it?
     
  2. do you have it wired correctly? i'm no help... i have no idea how that alternator is wired
     
  3. Is your power source to the fuse box switchd or B+

    [​IMG]
     
    Last edited: Dec 24, 2013
  4. 325w
    Joined: Feb 18, 2008
    Posts: 5,176

    325w
    Member
    from texas

    Maybe a diode in the white wire would stop it. It is for sure gonna leak all the electricity out.
     
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  5. 1950kale
    Joined: Jan 22, 2013
    Posts: 217

    1950kale

    so is the charging indicator lamp just like a normal light bulb? this same exact thing happened yesterday with another of the same alternators, but i took it to napa and got another one under warranty, and yes, the power source is switched, not B+. Is this alternator maybe not compatable with a non computer system? i think the damage is done & the hum is not fixable, but is there another way to wire this? does it actually HAVE to go through an indicator light?
     
  6. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    Member
    from Wisconsin

    Use a one wire alternator.
     
  7. 42merc
    Joined: Dec 19, 2010
    Posts: 600

    42merc
    Member

    It hums because it doesn't know the words.
     
  8. 53 sparky
    Joined: Feb 22, 2013
    Posts: 131

    53 sparky
    Member

    Ha!


    Posted using the Full Custom H.A.M.B. App!
     
  9. daliant
    Joined: Nov 25, 2009
    Posts: 674

    daliant
    Member

    lol !
     
  10. Acme Speed Shop
    Joined: Mar 31, 2007
    Posts: 1,755

    Acme Speed Shop
    MODERATOR
    from so cal

    Now that IS FUNNY!!!
     
  11. 325w
    Joined: Feb 18, 2008
    Posts: 5,176

    325w
    Member
    from texas

    Alternator does not care if you have a computer are not. It's humming because it's being told to charge and since the belts are not turning it it cannot charge. Yes the light bulb that was mentioned is just a regular single filament bulb like the other dash lights. You said if you remove the battery cable it stops humming. That is telling you it's getting feed back. You have to find the feed back and fix that. Are go to a one wire alternator.
     
  12. 63 Po-Po
    Joined: Dec 24, 2013
    Posts: 4

    63 Po-Po
    Member
    from Oklahoma

    Alternator is bad buy a one wire


    Posted using the Full Custom H.A.M.B. App!
     
  13. whtbaron
    Joined: Sep 12, 2012
    Posts: 541

    whtbaron
    Member
    from manitoba

    Hmmmmmmmmmmmm......
    You sure that replacement alternator wasn't for a Hummer?
     
  14. whtbaron
    Joined: Sep 12, 2012
    Posts: 541

    whtbaron
    Member
    from manitoba

    Ok... I'm trying to be serious now. The systems that I have added Delco alternators to have a constantly hot wire to the Bat terminal (and I like to see that a big one if you have major draws) with a constantly hot wire to the red terminal of the plug, and the white terminal gets switched with the ignition switch. The diagram above seems to switch both of the wires to the plugin. Not sure if that is going to make a difference, but that's what I'm seeing.
     
  15. BamaMav
    Joined: Jun 19, 2011
    Posts: 3,428

    BamaMav
    Member
    from Berry, AL


    That is the way I wire one, with the light going in the white terminal wire. I agree with 325 w, it's being told to charge because you have current going to the white terminal somehow.
     
  16. 1950kale
    Joined: Jan 22, 2013
    Posts: 217

    1950kale

    ok, my setup isnt the one in the diagram by themoose, mine has a plug with 4 inline wires, 1 big red one and 3 small ones, i was told to hook up the big red one to B+ power and ignore the next one cause it went to the old ECU, & hook up the next one to switch power, or an indicator light, and the last one i was told to ignore because it is supposed to go to the rev counter. but it still hums when the switch is off, ill check tomorro to see if it hums when the red wire is disconnected i think it will. but if its still giving me issues, ill try to hook up a 3 or 1 wire
     
  17. 325w
    Joined: Feb 18, 2008
    Posts: 5,176

    325w
    Member
    from texas

    You may have the 3 rd wire on switched power but it's still feed ing. Disconnect the white wire and the hum should stop. By using the light it breaks the circuit when not running.
     
  18. 1950kale
    Joined: Jan 22, 2013
    Posts: 217

    1950kale

    ok, even if i completely disconnect the plug, all it takes to hum is the big wire going to the B+ stud, even when the plug is completely disconnected & nothing is supplying power to that, so i think something is wrong, i think i burned something out when i hooked up the indicator light wire to switch power. this thing is bothering me, does anybody know of a 1 wire or 3 wire alternator that will bolt right in to where this one goes? but not be a pain int he a$$ to try to figure out, haha
     
  19. Bigchuck
    Joined: Oct 23, 2007
    Posts: 1,132

    Bigchuck
    Member
    from Austin, TX

  20. 325w
    Joined: Feb 18, 2008
    Posts: 5,176

    325w
    Member
    from texas

    Let's ask again. You have a 10ga. Are a 8 ga. Wire from the batt. post stud on the back of the alternator. Then you took the first are large wire in the alt. plug and ran it back down to the batt. Stud on back of the alt. then the third wire in the plug to the bulb that is inline to the ign. Switch. Is it possible to send a picture. Send to my email are pm for phone number.
     
  21. echnidna
    Joined: Aug 26, 2009
    Posts: 64

    echnidna
    Member
    from Australia

    either the wiring to the alternator is defective
    OR
    the alternator is defective, possibly a shorted exciter diode
    OR
    if it has an external regulator the regulator is defective
     
  22. 1950kale
    Joined: Jan 22, 2013
    Posts: 217

    1950kale

    ok i tried to send a picture & my done is sorta broken & i don't really have a camera, but ill try to figure something out, i think i wired it wrong and caused something to burn out, cause that happened to the last brand new alternator also, but i took it back and got another one under warranty, & same thing after i run it for a little. & yes big red wire went straight to the Bat stud on the back & the next wire & the last wire aren't used, the third wire or second to last from the big red one, i ran straight to switch power on the fuse panel, & it charged at 14.7 V, but when i turned off the engine, i happened to notice the faint hum & it didn't go away even when i unplugged the entire plug, its humming because of the battery cable going to the bat stud
     
  23. d2_willys
    Joined: Sep 8, 2007
    Posts: 4,094

    d2_willys
    Member
    from Kansas

    If the newer alternator is anything like a 10 or 12SI type, then one small wire is the field exciter wire and the other small wire is a sense wire. The sense wire should go directly to the closest connection of the battery + terminal. Not to the ignition side of ignition switch. What may be happening is that the alternator is always getting excitation voltage the way you have it wired.

    I would think the humm would go away if you pull the small wire plug. Sounds like the main diodes are cooked now. The battery is properly connected and not reversed, is it?

    Take the alternator and get it tested first. If ok (or replacing), then remove the wire on the ignition switch. Leave the bulb and other wire and see what happens.
     
  24. 1950kale
    Joined: Jan 22, 2013
    Posts: 217

    1950kale

    i just went ahead & bought a 1 wire alternato & made a bracket for that, now im gettin 14.5V at the battery,
    and it dosen't hum! haha so that problem is not taken care of, but thanks for the help guys i appreciate it
     

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