A SELSYN motor pair is used for tracking rotational position.  They work together as a pair, where one motor's shaft motion is transmitted to the second motor, whose shaft follows exactly the first.  One application example is a beam antenna position indicator, where the first motor tracks the position, and the second remote motor follows the rotation, indicating the position of the beam.  

This is a vintage used pair of GE Selsyn motors, tested and working as shown in the video.  One of the green leads on one of the stator windings is cut short, but still long enough to connect.

Simply connect all the wires from each motor together in parallel as shown in the table below. Then apply 115VAC to the two rotor leads.