I have a 2004 Mercedes c230 kompressor sedan with just 66,000 miles on it . The last two days I have been getting the red battery /alternator light , last month the voltage was 12.9 ,now the voltage reads 11.7 , and if I turn the wipers or radio on the battery/alternator light comes on and keeps flashing . Is this the alternator or the voltage regulator ,or should I just change the alternator since it is connected to the voltage regulator ? Please help !!!!!