vaj4088:
How are you planning to step DOWN from 11 volts to 12 volts?Caution: Some automotive electrical systems have brief excursions to almost 50 volts that will not show up in a casual measurement but can destroy electronics.
What car (manufacturer, model, year, engine, other details), and how did you make the measurement?
I don't know that I can be of much help but perhaps others will help.
I was trying to keep my post brief because I tend to write long posts. The car is a 2002 BMW 325i. I just used a standard multimeter and took a reading when the engine was off, during start-up, and when on. I do know about the spikes and if the alternator goes bad, it could stay at a high voltage too. I don't need it to step down less than 12v since I will have a lipo battery pack to keep it going when the car is off.