Navi screen gets dark when headlights are turned on

Well, it's normal for the Nav screen to dim when the headlights are on, but not to the point of barely being able to see it. When you say "brightness knob", are you talking about the one that adjusts the brightness of ALL the dash lights? That's the wrong one.

You can adjust the Nav screen brightness via the SETUP menu. In addition to a touch-screen brightness scale, there are preset buttons: Auto - brigher w/o headlights, dimmer with; Day - always brighter (always the same); Night - always dimmer (always the same).

Yes there should be a ...

... noticeable difference in brightness. But it should still be very readable. The "daylight" screen would be too distracting for night driving. But as I said it should look very readable and "natural" at night.

If you like the navi screen bright.....

then go to the navi screen set up, and leave the day setting on, take it out from auto, so regardless if you have the headlights on it will stay the same brightness.

Thanks for the info ...

... I always learn something on this site.