Have a Lexus gs300 1999 and it was running good till a rainy day and flooded the engine so i changed the oil and pump the water out and knocking became a thing but we thought it bent a valve since the noise was coming from up top of the engine so got head completely done then put everything back together and fired right up but knocking was still there so now we completely took apart engine and was a bent rod and a loose bearing connection so completely rebuilt the engine from pistons to seals all the way up and put engine together when I went to connect battery at 1am after finishing i connected it backwards so i went checking cable by cable to see which one is burned or bad found a blown 02 sensor cable so i cut and rewired and then cranked wouldn't turn on so i just went to local junk yard bought engine harness and put on only cranked then so i checked fuel pump and it wasent getting power so i sent direct power tp fuel pump from battery and got it working thru switch and that switch gave power to other things aswell so i cranked engine and it stays on for about 2 seconds and dies so idk what to do please help need loads of suggestions thank u.