the bulb is fine because its lights up it wont go off when the switch is in the middle position
Does the light go out when the switch is moved to the Off position?
Removing the two screws will allow the ceiling light assembly to drop down. There's a three pin connector between the assembly and the ceiling wiring harness. (I don't think the screws provide a ground for the light because that would negate the role of the BIU; however, it's possible that a wire was crimped by a screw during assembly, and is grounded when it should not be.
At the connector, pin 1 should be a black wire. This goes to ground.
Pin 2 (center pin) should have a brown wire. This goes to the Body Integrated Unit, which grounds the light when a door is opened, and turns the light off when all doors are closed (when the switch is in the "door" position).
The last pin, #3, should have a blue wire with a red stripe. This is an always-on 12 V (when the battery is connected).
Let us know what you find.