Chevy 1994 p30

I have replaced the alternator and battery, what circuit is used to excite the alternator to give out put. there are 4 circuits wired into that one littel wire according to the woring diagram. I have also read of the alternator light does not come on that is the dround for that wire. the check engine light does come on when the voltage gets low. any help would be great. This is in a rv but it is a chevy p30 chassi with 454.