The handlebar has a display for switching motor on/off and for selecting one of three speeds. Even when I switch this off the motor then decides to work and races away. I can then only stop by applying brakes and switching battery off with key. On switching back on, the display lights again but motor will not work unless I give bike a good shake, it then works normally for a while but soon races away uncontrollably after a short time, back to square one!