Are you just supplying power with a battery charger? That sounds like a bad idea, you want a good battery to start with, and a good volt meter
I have never messed with s flooded truck, but I would be starting with the computer, they will not standup to water
Try unhooking everything not required for the motor and start tracking power for that
Don’t worry about lights amd such
Did you pull the seats? , there is a computer under there on mine.
I presume you have all the flooring out of it, that stuff could be pressure washed and dried after you get it running
Would a good code reader help?
I am not up on those