Hi great read and very useful. I have a VW transporter that gives battery voltage to the D+ wire until you connect it then its 1.6v regardless of engine running or not. Light stays on and no charge. Make up a wire direct from battery + with an inline bulb and this extinguishes when the engine starts and new alternator charges fine?

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This post was auto-generated based upon a question asked on our tech article page here: Pelican Technical Article: Alternator System Troubleshooting

[Wayne 962]

I'm not a super alternator expert, but I believe that you will see this behavior when the diodes in the alternator fail. The light will sometimes stay on all the time, and you may even run your battery down from the light being on all the time. The solution is to replace the three or so diodes in your alternator - I think that will fix your issue.

- Wayne