Arched the battery pos to neg?

My buddy was hooking up aftermarket speakers and amp to car and said he arched the battery pos to neg. Ever since then no crank no start. Checked all fuses and relays. I replaced ignition switch, mega fuse going from under hood fuse box to alternator, and battery current sensor. Had no instrument cluster lights. Found that the battery was dropping massive voltage when I turned the key as well. I swapped out the ecm from flashmasters yesterday and still getting nothing. Please if you can help me im tired. Oh and this idiot also thought it be a good idea to remove the whole fuse panel from the trunk and take out all fuses at the same time and they all got put back wrong. I followed the diagram the best I could and hope I put them all back in the correct location