PROBLEM SOLVED!!!!!!!!
Hi, i too had have an LG G5 that was dropped in water back in January, After that day my backlight never worked the same. either it didn't work or it was so dim that i could only use it in doors. in addition my headphone jack was crap. so i decided to take my phone apart and clean the contacts ( i used to fix phones for fun so im pretty comfortable taking it apart). I spent alot of time cleaning the contacts for the screen. i cannot stress this enough make sure you get them as clean as possible. my cleaning tools were a very small flat head screw driver, Qtip and cologne ( mine has alcohol in it). After cleaning, plug your battery in to the charger without placing it in the phone, so its just the speaker deck and battery plugged to the wall. Next take the phone (with the phone still out of the body) and gently slide the battery into its place. the screen should light up with a charging sign, (Now this is the trick) If your LCD doesnt light up but the orange light appears indicating that the phone is charging, lightly press on the top of the screen connecting cable on the motherboard. the pins towards the top control the screen brightness. if this does the trick and your screen lights up then you are ready for the next step. now what i did next was take some tape stuck in the phone body right where the screen cable would rest so when the phone is assembled the tape presses agains the screen connecting cable. Good Luck