The imbalance in pressure is from front to rear. If you have the correct master cylinder on the car there is a reset button on the side of the cylinder its self that resets the light on the dash if it is on from an imbalance of pressure from front to rear. Just push th plunger on the switch back in to reset the circuit. Check fluid level in master cylinder if it is not low, remove plug in at front portion of master cylinder reservoir (front float assy) if light goes out check the float for being disconnected from shaft. Do same thing for rear float on reservoir. As for calipers on front, both sizes of pistons were used, depending on brand. What is important is that both sides are the same size and brand. I would pick out the dry one or the one that looks best, and match it with one for the other side.