I have a 03 BMW 325I and recently had a pulley tensioner to break offbecause someone used a mechanical one instead of hydrolic onecausing my belt to come off and engine to overheat. Since then I had it repaired but now my battery light is staying on. Is it possible that the belt has been put back on wrong and making my alternator turn backwards and causing the light to eluminate?

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This post was auto-generated based upon a question asked on our tech article page here: Pelican Technical Article: Troubleshooting Electrical Problems on Your BMW

It's not likely that the belt can be put on backwards - check out the belt article in our tech articles section for the proper routing of the belt for your car. I'm not sure what the could be exactly, you'll have to check the alternator to make sure it's still charging properly.

- Wayne

Belt tension may be not tight enough such that the engine turns but the ALT was not adjusted after the new tensioner causing the belt to slip on the ALT pulley. a slipping belt can cause a no charge/ ALT light on. The ALT is not turning backwards it is not turning enough or the diodes/regulator/ALt is bad...

Have you tested the voltage of the car at the Hot post in the engine compartment. Off and at over 1800rpm...
Off should be 12.4 or so and at speed should be over 13.4 (values are estimates)?