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Thread: Alternator overcharging, but alternator tested good??

  1. #1
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    Aug 2010
    San Francisco

    Default Alternator overcharging, but alternator tested good??

    Hi, I have a 1973 240z, rewired the car with an EZ wire harness, and I have upgraded to a 60 amp alternator from a 280zx. I've driven the car fine until I had an issue of the alternator overcharging. The original 60 amp ended up testing bad, so I replaced it, and made sure to test the new (re-manufactured ) one I got. It tested fine, but when I installed it in the car, I hooked up a multi-meter and it was going up to 15.7 even after warming the car up, and putting load on it, including lights and an electrical fuel pump. Anybody have any idea what could cause this? Such as a wire too small going into the voltage regulator, or just an alternator that instantly went bad? Or something else? Thanks for any help!

  2. #2
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    Oct 2009
    Washington County, OR


    Maybe you have bad connection on the S wire. The internal regulator uses the S wire to set output, raising output until S is at the set point.

    You can test it by running a jumper from the S terminal directly to the battery positive or the starter solenoid lug. If voltage drops to normal, then your S wire has a bad connection.

    I've had a bad connection right at the T connector on the alternator. You might just clean that up and make sure it's tight also.
    Last edited by Zed Head; 02-07-2014 at 11:04 AM.
    1976 280Z, with some minor modifications

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