Hey master mechanics out there

I just wanted to ask some questions because I’m not sure what to do from here.

What should I test next?
Do you know pacifically what relays and fuses I can check?

My 2015 Ford F-150 3.5 Ecoboost has no power whatsoever; nothing happens when you open the door or hit the start button. No accessory power, nothing.

Yesterday, I was wiring a six-gauge power cord from the battery behind the fuse box through the black boot into the passenger side floor. I used a screwdriver and a pick to make a hole through the boot, and wire tape and soap to safely pull the cord through. Then I ran it to the back of the truck where I wanted to put the amp for my subwoofer. I never disconnected the negative battery terminal, stupidly, but I only briefly left the positive six-gauge power cord connected to the battery to see if it would fit. I didn’t have anything connected to the six-gauge power cord when I tested the fit on the positive battery terminal. After that, I wired an output converter to the existing factory subwoofer wiring, and when I went to shut my door, I noticed my running boards didn’t retract, and I had no power to the truck. I attempted to start the vehicle, but nothing happened. So far, I have tested the fuses and swapped relays, but nothing has happened. I’ve noticed that the fuses in the inside fuse box and the under-hood fuse box have a burnt substance on the plug, but they pass the multimeter test.

I just had the battery tested today. It has 100% charge but failed the cranking test.

made a post yesterday this post is much more detailed hopefully you guys can help thank you