Car dies when I unhook battery. New alt

Posted by frankozz, Nov 22, 2008

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  1. frankozz

    frankozz Proven Member

    Joined Aug 21, 2008
    san diego, California
    A few weeks ago my car died on the way to work. First the lights started to get dim, then they got dimmer and dimmer. Then it died. I tried to start it again and it would crank just fine at first, then slower and slower and then it would just make a fast clicking sound. I was told it was my alternator.

    So I got a brand new alternator from autozone, put it in a few minutes ago, crank my car, it starts, everything was fine. I've heard that a way to test the alternator on a car is to unhook the battery, if the car stays running, the alternator is just fine, if the car dies, alternator is crap. So I unhooked the battery and the car died WTF? Why? the alternator is brand spanking new! I also took my battery to autozone to recharge it and test it. It was still a good batery. Anything else that can be causing this?

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  2. steve

    steve DSM Wiseman

    Joined Feb 3, 2002
    St. Charles, Illinois
    First, that test can damage your car's electrical system. It was ok back when we had points, and mechanical voltage regulators but it's not anymore.

    If you searched here you would have seen the tests to make sure than your alternator fuse was good.
    You need to check it, measure the voltage at the battery with the car off and again with it running, and at the B+ stud on the alternator in both cases.
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  3. DSM1G90

    DSM1G90 Supporting Member

    Joined Apr 6, 2008
    Nampa, Idaho
    ? ...why do people goto "Autocrap" for car parts instead of something better like Napa..?

    Autozone = "Wal-Mart" for car substandard.

    But, do agree: not healthy on an ALT when you disconnect a battery while in operation. You could have toasted that ALT.
  4. Julioluko

    Julioluko Proven Member

    Joined Dec 29, 2003
    Midland, Michigan
    Yes you can damage you alternator by just unhooking it, it puts too much load on it and it will burn it up, you didn't do this by that simple test. Just check your fuses in the engine bay and in the car. If you want to make sure the alternator is good Auto zone or Advance Auto can test it while its on the car. Its its found to be faulty they will replace it for you. Auto zone is kind of the Walmart of part places, but just as in Walmart not everything is that bad, most of the stuff is made by the same people that make it for the stores. Each store you go to has its items that are great parts, Napa's axles are ten time the quality of CCT axles sold by Auto Zone and Advanced, Advanced Auto Permatech gaskets which are awesome, and Autozone has their high end brakes (their cheap one are really bad though) its all what you want to pay for.
  5. DangrousDave20

    DangrousDave20 Probationary Member

    Joined Jul 7, 2009
    Picayune, Mississippi
    So did you figure out what was the problem?? Because I too just bought a new alternator, installed it, and disconnected the battery after the car was started and it died. I've heard people on here say you need the battery to keep the engine running, and some say you don't, that the car will run without the battery altogether. Which is right??
  6. canada4g63

    canada4g63 Proven Member

    Joined Jun 6, 2009
    Cleveland, Ohio
    check your ground and your battery terminals for grim, and brush it off.
  7. the_mork

    the_mork Moderator

    Joined Mar 10, 2008
    Eau Claire, Wisconsin
    Mine used to die when I just had a bad battery let alone what would have happened if I unhooked it. By the way in case you missed the second post in the thread...

    Don't unhook the battery while the car is running.
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    93ETGOCART Proven Member

    Joined Aug 28, 2008
    stotts city, Missouri
    you can buy a black and decker battery charger than can test your alternator. but the make a good point check your fuse if its just a little cracked it can kinda work with enough juice to shoot the gap.
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  9. Defiant

    Defiant DSM Wiseman

    Joined Jan 13, 2003
    glorious Galt, California
    Not on anything since the eighties.

    Sounds like your new rebuild is crap. Common.
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