You can control three brightness settings for the button/knob leds:

1: Hijack menu allows setting the "on" brightness, including completely off.

2. Hijack by default will dim halfway from "on" if you turn on the headlamps, but one can override this with an exact value (including off) in config.ini.

3. Another Hijack config.ini option sets what happens when the player is turned off. By default the buttons stay dimly lit.