Ciao Leonardo,
sorry for writing you in english, but I'm coming from germany and can't speak italian.
Please have a look here:
https://www.thingiverse.com/groups/thingiverse/forums/general/topic:49300
and
https://github.com/knutwurst/Marlin-2-0-x-Anycubic-i3-MEGA-S#readme---english
I have the same motherboard and flashed this file:
https://github.com/knutwurst/Marlin-2-0-x-Anycubic-i3-MEGA-S/releases/download/1.1.9/MEGA_S_DGUS_BLT_10_v1.1.9.hex
My BLTouch is connected to the 5V-GND-S1 connector. I had to switch the 5V and GND cable and now everything is working fine.