Moonzy - I am researching the i5601E display for total fuel consumed / trip and came across your post.
I think this may answer your question, many years later.
Lighting and Contrast
The backlight intensity and contrast settings for the i5600 display can
be adjusted by briefly pressing the last Screen Softkey on the right
while viewing any instrument gauge screen. Doing so causes the
Lighting & Contrast Pop-up Menu to appear at the bottom of the LCD
display. Press the softkey directly below the softkey cue for the
adjustment desired and the display will immediately adjust according
to your selection. Continue making these adjustments until you have
achieved the optimum viewing settings for readability. Press the
softkey under EXIT to leave the Lighting & Contrast Pop-up Menu
and return to the screen you were viewing prior to making the display
adjustments.
If brightness and contrast are accidentally set so that the Lighting &
Contrast Pop-up Menu is no longer readable, press the four leftmost
softkeys simultaneously. This will reset the contrast to a readable
medium value and the backlighting to 100%.
