car is surging and electrical is going frits

Hello everyone, I own a 2003 Mustang GT, my issue is me and my buddy took the motor apart all the way down to the valve covers and put it back together everything was torqued to spec once done. we put water in the reservoir, and put my jumper box on the battery as it was dead, It fired up and we took the jumper cables off. and drove it not even 2 miles, after the road test the water boiled bad and blew all over everything. We shut the car off and left it to sit for a little while to cool down. after some time, I got a new thermostat and new O-ring as they were toast. Once we installed the new stuff and put actual coolant in the system, we started it. This is where everything went bad, the car had to be jumped in order to start again, so we did that and it started surging and the gauges would go to their max point and go down a 1/8th of the way in a fast motion, my SCT Tuner would turn on and off in the blink of an eye repeatedly, so I shut the car off immediately. I don't have video as I'm nervous to start it back up. when I disconnect the jumper box there's no power whatsoever(havent disconnected the jumper box when started only the one time). I feel like the battery is just bad but I feel its more then just a bad battery(maybe wiring harness is bad or fuses are shot who knows). I want to see ya'lls thoughts on this, and no I haven't checked the fuses yet, going to do that tomorrow.