Question about 2003 Volkswagen Jetta TDI

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2003 Jetta TDI alternator light came on in dash

Removed alternator and had alternator checked - alternator was good.
Found out that there was no power to the control wire on alternator.
Checked all the fuses in the fuse box, checked the fuses under the dash. Where do I go to next?

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  • mamaruthie Jun 27, 2009

    I traced the control lead backward, but could not find the regulator in the little cluster.

  • Anonymous Mar 22, 2014

    alternator not charging. should have power, key on, on the blue wire on back of alt, I do not. is there a fuse, or is it controlled by the pcm?


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Your voltage regulator supplies the path for the control lead of the alternator and varies the amount of current available to provide the magnetic field of the armature with the required strength. Measuring from this lead to ground won't show much voltage.
Apparently the regulator is not integrated into the alternator and is probably failed. If you can chase the control lead backward, you will find the regulator and these are mostly mounted on the fender well or firewall.

Posted on Jun 27, 2009

  • Steve Allison
    Steve Allison Jun 28, 2009

    For your current dilemma and as a valuable resource for future problems, check your local library for, or purchase, an aftermarket service manual from Haynes (1st choice) or Chilton. They are richly illustrated and cost between $20-$30 US and available at auto parts stores.
    They contain detail such as the location of the voltage regulator and generally supply clearly written test information for this kind of troubleshooting.


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