The transformer usually consists of three windings, a primary and two or more secondaries. The primary is supplied with 110 VAC from the plugin.The primary produces a magnetic field in the transformer's iron core, which in turn causes currents to flow in the secondary coils which are wound to produce lower voltages than that applied to the primary. One secondary produces a very low voltage for all the lights (usually 6 volts) while the other operated all coils and motors (usually 25, 30 or 50 volts, depending on the manufacturer).

The outputs of the secondaries feed the "power lines" to the other game components. One side of the secondary supplying the coil voltage feeds the "coil common" line which is usually connected directly to every coil in the game. The other side is connected to the "return line". Various control switches connect between this line and the other side of the coils.

Similar connections are made to the other secondary but there are light bulbs acting as the loads rather than coils.