I installed an alternator a month ago and it's been running well until today. The battery light is on and the voltage is running around 16-17 on the dash board. This truck has an internally mounted voltage regulator on the alternator. Could this be the culprit?

 

More than likely it is.
The other thing would be high resistance (or open) on the "A" wire from the alternator to the battery (bad plug?).

 

The final verdict was the voltage regulator. Advanced Auto replaced the alternator with no questions. The voltage runs where it should now with no battery light. Thank you for the support.