2002 Excursion 7.3, Getting 12 volts at fast idle 1100 rpm no load. 8 volts under full load. Gages and radio etc cutting in and out. My question is, is there a voltage regulator i should check first or should i start with the alternator ? Not sure if there is even a voltage regulator what should I check/test first, New to me truck in Nov this year so not to sure how old the alternator is.