Zigmoto

In the middle of swapping a 4.6 2v into my 2003 v6 chassis. Engine is a Windsor from early 01 car using a late 01 automatic engine, pcm and starter harnesses. When I turn the key on initially I am able to use windows, gauges radio, etc. Even was able to put a tune onto the ecu to remove pats. When I try to start the car all I hear is a pop from the speakers and I lose all power. If I disconnect and reconnect the positive battery cable it will regain power but the same thing happens everytime. I tried adding another engine ground from engine to frame as I did not have one. When I did this I noticed that power will cut out a few second after even turning the key to first position and radio never even turns on. Removing the Ground I added let’s it go back to radio working and power until attempting to start. Would this mean I have power shorting to the frame? Or what could the issue be? Any advice is greatly appreciated