might be body control module as is common for the circuit soldered relays to fail and can do so and prevent the main power relay to switch its self off ,, could try this lock the car while sat in side and after 3 minutes you should get a click noise if its working right,,, ie this will be the body control module going the sleep ,, if no click then would say have a bcm issue,,I’ve got an issue with my Mini Cooper 2004 base model 1.6L. It’s sounds like the mini is bussing. It might have a electrical issues somewhere. something must still be on. When it’s in accesoria mode it ultimately will drain the whole battery, if I leave the ground plugged in. Has anyone had any similar issue where i take the key out of the car and the brake light come on.