If the Bulls is like my Cannondale, with a Bosch Gen4 motor, this has to be done with the Bosch diagnostic at a Bosch or Bulls dealer. The two options are "always on" (speed pedelec European regulation), or "last state". When set to "last state", the Kiox turns the lights on and off, and the handlebar button cycles between low and high. Off means off though, including both the taillight and stop modes on the rear light. At least my bike works this way. I wish I could have the tail light on all the time, with only the headlight under control. That would take running a separate wire to the taillight from the motor, which I will do at some point.