"This cable allows you to power the new 9v motors from the old 9v system or vise versa.. I am a keen collector of lego 9v trains and as any collector knows , the old 9v system train motors are getting expensive to get hold of. When you use 2 motors to power a train this cable lets you use a old 9v motor and a new style motor as used with the new RC controlled trains , with the old style train transformer ."