my dad has a 07.5 6.7 mega cab and his fuel in water light keeps coming on we have drained the water and fuel seperator and changed filter and hes put straight number one in on one tank and multiple additives in and the light will not go off but. if he is driving along hitting the throttle the light will go off and when he lets off it will come back on. it wont do it all the time but always does it when hes on the highway or interstate.