I just purchased a AC/DC clamp meter that measures AC/DC amps and does volts and continuity and stuff like that and i put the clamp over the large charge wire coming from the back of the alternator and my alternator started charging from the moment the truck started, it was putting out 75 AMPS at very rough idle. I was gonna post a video but i didnt wanna run my truck again until i get the rough running condition fixed as i dont wanna damage anything while running with a bad injector. It makes sense though why the voltage acts the way it does until the glow plugs shut off as the glow plugs use 10 to 12 amps each and worst case they are using 96 amps so it would stand to reason that the battery voltage is pulled down until they shut off.