This supply is a rejuvenation of one provided several years ago, but with current components.  It is designed to replace the exsiting battery used to operate the horn and some other limited applicaions in post-war Lionel applicaions.  The supply has three wires to connect to the center rail, outside rail, and battery connection on the relay.  Details provided in the accompanying instructions.   Mounting is via a double-sided tape.  This approach supports future removal if necessary.