Use 4awg wire when you connect all the wiring for the second alternator. Can't really give you any help on the subject beyond that except a link to a short tutorial on adding a second alternator.
Igitur qui desiderat pacem, praeparet bellum -- Vegetius
"I told her about my conversation three years ago with the political leader of Islamic Jihad in Gaza. "What's the difference between suicide, which the Koran condemns, and martyrdom?" I asked. "Suicide," he replied, "is done out of despair. But remember: most of our martyrs today were very successful in their earthly lives." In short, there was a future to live for--and they detonated it anyway."