If your vehicle is showing interior dome light won't turn off and drains battery, here are the most likely causes and the parts you'll need to fix each one.
The interior dashboard dimmer switch is often accidentally rolled past its detent into the 'always on' override position. If it's not user error, the switch itself may have failed internally.
The small pin switch located in the door frame detects when the door is closed. If the switch breaks, sticks, or loses its rubber bumper pad, the vehicle will think a door is permanently open.
In many modern vehicles, the door ajar sensor is built directly into the door latch mechanism. If the latch gets dirty, jammed, or fails electrically, it will continuously trigger the dome light.
The relay responsible for keeping the interior lights on for a few seconds after closing the doors can have its internal contacts fuse together, keeping power flowing continuously.
The main computer that controls body electronics can develop a short in its interior lighting circuit. This is a rare but expensive electrical failure that forces the lights to stay on.