The Stovebolt Site Forums The Shop Area The Electrical Bay alternator warning light.

I also had this problem.
It seems the regulators on many alternators are configured to control an incandescent bulb rather than an LED.
They raise the voltage on one side of the bulb, but not enough to turn off an LED which will still illuminate under a small voltage difference.

I bet if you swap in an incandescent it will be fine.