If your dc to dc converter is wired incorrectly, disconnecting your MBB to key circuit wouldnt do anything about the lights coming on at all times. Does it have a contactor or solenoid? Is it a sevcon controller or alltrax? you need to confirm exactly what bike you have because 2012 was a weird era. you could have a brushed or brushless motor, a leftover 2011 bike etc etc.