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Alternator bad?

Discussion in 'General Chevy & GM Tech Questions' started by jdusmc214, Nov 13, 2010.

  1. jdusmc214

    jdusmc214 New Member

    If when I roll my windows down, the headlights dim, is my alternator going bad? This seems to happen whenever I use 2 things at once.
  2. MightyMax

    MightyMax Rockstar 100 Posts

    Could be a sign of weak alternator.

    How old is the battery??
    If over 3 years, it could be in that questionable area.
    If over 5, then time to replace him.

    Get a Multimeter, and check your voltage at the battery engine off,
    Then engine check the voltage.
    Then check the voltage at the alternator while have someone lower the windows and lights on.

    Also make sure your belt is good...may be time to replace him.
  3. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    X2!! also do they only dim at idle or when you are driving down the highway, because if those things all test good then there is a chance that you have a bad gorund. And to add to the above you will also want to clean the terminals for the battery since corrosion on the terminals can cause this as well.
  4. MightyMax

    MightyMax Rockstar 100 Posts


    That was the one I forgot to add.
    Thanks murdog.

    But if your terminals are heavily corroded, that builds up a resistance to the voltage coming from your alternator.

    Just had this problem w/ my corolla
    So clean and sand the terminals. ;)
  5. jdusmc214

    jdusmc214 New Member

    I just replaced the battery a few months ago. I have noticed the lights dim a little while I was driving, and without doing anything else, like the windows or heater/ac. How, and where do I check for a bad ground?
  6. MightyMax

    MightyMax Rockstar 100 Posts

    For your charging system,
    It should be your chasis ground, which will be on the fender well (usually) or somewhere in that area.

    Getting a Volt meter would really help a lot
    Then you can see if you are getting proper voltage at least.....

    Also, trace your wires for your lights....
    You could have some bare wires that are grounding out....that will have a draw on your voltage...
    Again, I highly recommend getting a volt meter.
    Then you can rule out a couple things real quick by getting the voltage readings.
  7. silverhobey

    silverhobey Rockstar 3 Years 500 Posts

    i know someone mentioned Alternator Belt---make sure it is tight before you try removing it to check for wear-----if you have to buy an alternator, usuallly get a core charge when you return your old one----I haven't ever had to replace one in my 22 years of working on my own vehicles, but shouldn't be too hard if you DIY.....good luck in whatever you find

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