I have the same idiot light on. "External Lighting". Thanks for the ideas in this thread. I also noted today that the headlights stayed on after the car was shut off for an extended period Weird. Also the courtesy lights do not dim and shut off with the doors closed when in Auto position.
Update! have been reading about trunk water leaks affecting the locking system. Sounds so similar to my problems, so I will investigate. Its raining as we speak!

Update. April 21 2022 I tore my trunk apart (bad move) and found the trunk and air pump dry as a bone, no problems there. In re-assmbling the passenger side window trim, I have yet to get it on properly. Found numerous broken plasticy things from a previous attempt, and I had to stop trying to save my sanity. I will try again but any hints on getting the trim back in place would be appreciated.