the way a duel MC and proportioning valve works is, if a front or rear wheel cylinder blows out then the proportioning valve will shut off the pressure to the wheel that has the problem, so you can still stop on the good brakes. if you have the pressure switch in the rear line behind the proportioning valve and the rear blows out and the pressure is cut off to the rear wheels then you want have any break lights. to have brake lights all the time you will need 2 pressure switched at the MC or 1 elec. switch.