I vote for the battery itself of the voltage regulator. Check battery voltage with car off. About 12.4? Check battery voltage with car on. About 13.8? If not, then you aren't charging. If it IS charging, then battery isn't holding a charge very well. Take battery out and have it tested at local auto store - they can tell you if it is not holding charge. I recently returned a 2 year old battery for free replacement. And it was a top of the line battery.