Y cables are used to attach two servos to one output. Both servos will move in the same manner at the same time. Could be used, for example, to control a crossover or a passing siding. Does not affect the servo power. The Y can can also be used with the fascia controllers for the Quad-Pic to provide two control points for one switch. Use one for a pair of servos and one for a controller at the same time and you can set up a passing siding with control points at both ends!