First time ls/vortec swapaper, please point out the obvious for me :)

[atotalnincompoop]

I have a mickey mouse standalone harness that I had made by some dude on ebay out of my stock 99 gmc harness that I harvested my 4.8 out of.
The guy offers ZERO tech support and no instructions so I have a few questions, I'll post them one at a time and address each issue and resolve it before tackling the next.
I have an aftermarket 21 circuit wiring harness in my 55 gmc. This harness has an alternator exciter wire and an alternator power wire. The standalone harness has a single wire that plugs into the alt. Is that the exciter wire? Do I need the exciter wire from the 21 circuit harness or do the pcm control that.
The alternator is the stock unit from the 4.8 truck engine.
Thnx ☺