Red battery light is ON when the car stop.

Hi everyone, i am a newbi here.

I have a Volkswagen Jetta 04 and i have been trying to fix my charging system. I have couple of questions, perhaps someone can help:

couple of days ago my red battery light would turn on when i would stop the car. Yesterday the battery died. I have replaced the battery and the alternator, the car runs but the battery light still comes up when the car is stopped.

I took a reading with my volt meter at the battery this is what i get:

12.7V - Car is off.
12.1V - Car is in idle (sometimes the V drops to 11.9V)

I don't know what else could be the problem. any ideas what could be the problem.

Thank you in advance,

-Jay

P.S. any idea where the to small wires from the alternator go?