mechman not charging

So I haven't been on for a while I was in a car accident today I was able to get some energy to get started on my truck again, first thing was first, the alt, mechman 270, got it hooked up and wired up with big 2 ran my power cables today and when I turned on the truck the voltage stayed at 12.7 baffled, so I figured I take out my amp and put a load on the electrical system to seeaybe 12.8 was going to be my charging voltage, nope the voltage dropped and got no higher again, the factory alt had the 3 pin oval with an extra yellow lead from the factory harness, I've looked for what this wire is connect ted to and can't find anything