Had a wierd short. Cause even weirder issue

[Oteroluis98]

So my positive battery cable melted in the little
Junction box next to the alternator melted till it grounded . I was unaware and was able to make it home no problems next morning I tried to start it runs for 2 seconds shutsoff .I fixed the short checked fuses , I have replaced the pcm and put my original tune back In and same issue . I turn the key to the run and all I get is a battery light I start it and the dash lights up as if a barely set it to run the truck shuts of then the dash shuts off 1-2 seconds afterward . I was able to get the truck to run but I have to disable the vats completely with a stock tune and before programming I have to unplug the bcm .when I unplug the bcm the dash does turn on like normal. I tried another bcm but I have same issue does anyone know what it could be?

[gtstorey]

Still need to post tune and log and more details of what you are actually working on.

What is the voltage doing during this time?