The cable selector is the checkbox next to each cable. There is a master checkbox at the top of all the cables that you can use to select or deselect all cables at once (indicated by the arrow in the picture below). Each check box can be selected/deselected individually. The check box works in conjunction with the reset button, script manager and send commands options. If a cable is not selected it will not be reset and will not receive commands from the send commands box or from the script manager. It is like the cable is not in play.