The front reservoir should supply the front brakes...and rear reservoir for rear brakes. Like Evolvo said it wont matter if you plumb the fronts to the left side and rears to the right side or vice versa...as long as the front reservoir supplies the front, and rear resevoir supplies the rear. I plugged the 2 unused holes and just ran 1 line out of each side to a T fitting...makes for a cleaner looking install.