Headlights stay on

I have a 2009 Gen II Prius and the headlights started to stay on. The only way to turn the lights off is to disconnect the 12V battery and as soon as it is reconnected the lights come back on. It is only the headlights and the car runs fine otherwise, it is just annoying to keep disconnecting and reconnecting the battery. Also the light is dimmer than the normal or high beam setting, both work perfectly. When I use the steering wheel to manually turn off the lights it just gets dimmer but refuses to turn off.