Use this wire to connect your speed regulator to your tracks and give your train the power it needs to get rolling! 9v LEGO Trains require 9v tracks and rails, which conduct electricity. Compatible tracks and rails are #4515, #4519, #4520, #4531 and any track collections consisting of these item numbers. When motorized with a 9v motor, this engine will not run on LEGO RC Train tracks (#7895, #7896, #K7895, #K7896).