My car will stalls whenever I turn the headlights on but it runs normal when I have them off during the day. What seems to be the problem here? The alternator seems fine cause it still recharge the battery and such...or could it still be the alternator?

 

could be a problem with the voltage regulator, try swapping in another alternator, see if the problem goes away

 

I've a volt meter hooked up and it start with 13.9 and after a while a min or so (idling), the voltage will drop to 13.5 or less and then the car will stall...