Remove the logic board and charging board, and clean any liquid damage using 95%+ isopropyl. If you are getting a charger light when a charger plugged in, it is likely the trackpad cable (check both ends, if burnt or liquid damaged, replace), trackpad PCB (check for burns or corrosion) or most likely the keyboard.
If there is no light on the charger, check the I/O cable for burnt pins. It could be the I/O cable, charging board, keyboard (shorting PP3V42_G3H to ground) or PP3V42_G3H is not being produced on the logic board, or is being shorted to ground.
Clean any liquid on the board first, but take a picture of where it is corroded before cleaning. If no liquid on the board, most likely will be the keyboard, if the charger is lighting up and the trackpad cable is fine.