Hi Trussman,
Stan is correct. To wire the MTH crossing gates to an insulated rail (your rail "A") you will need a relay that can power both the "UP" and "DOWN" circuits. One option is to use a Z-Stuff DZ-1008A relay, which is available from many train retailers. Here's a wiring diagram that shows you how to wire the MTH gates with a DZ-1008A to an insulated rail.