Hello milobob,
To bad it is not that easy...
The knob you refer to dims both daschboard and radio.
Problem is if setting is at max (bright on dashb.) radio is to dimm.
If dashb. is set to bit lower setting radio light is almost gone
This hapens as well with as without headlights.
I found out more have this problem, but no (acceptable) solution.
Judging your remark, you dont have it? do you have an outlander 2007??
Sorry for my english, I am dutch
Unfortunately the Lancer and Outlander suffer from this problem. I have no knowledge of a fix either. Unless you change the stock radio to perhaps a custom double din display like the MMCS... or somehow set the display back, I don't think an amount of light intensity from the display will fix the problem when the sunlight is directly shining onto it.