I have an 03 GT and my voltage seems to fluctuate a lot. sometimes I have even seen it drop to almost 12 Volts when a lot of power is drawn (when A/C compressor kicks in, both windows going up or down, etc.). What I wondered about the most though is when I press the brakes I can see my lights dimm and a drop in voltage. Is this normal for these cars? I have had the alt. replaced and everything checked.