Hi Bartolomeo, I don´t have photos, but the original WAS has 4 pin plug (under radiator, right side) and 3 pins are used: +5v, gnd, and signal. You must disconnect +5v and gnd, connect them with same power that powers arduino and you need to make by-pass on signal wire.
I don´t have any problems with it. Maybe on newer tractors there will be, because of disconnecting +5 and gnd.