5.7 Alternator HELP!!!!

Ok so here is what's going on. I got a nearly new allternator from my dad off of his 5.7 truck engine. I have mounted it to the 440 in my dart. My question is, what do I need to do to get this thing to work! I have looked over the wiring diagram for the truck and found that one wire in the connector goes to ground and the other goes to the pcm. I can't figure out what exactly the ecm does to control the alternator. I have supplied 12 volts to that terminal and it full fields it, charges up to 17 volts! I'm thinking maybe it just needs a 5 volt reference? I would really like to figure this thing out. I posted this in the electrical section as well, but I figured maybe someone has done this and made it work with their hemi swap. Please help!