Dash lights not working

I see no corrosion of even evidence of anything getting wet on either side where the wiring passes from the door nor inside beneath the dash. I'm taking it to a dealer. I don't have time for this. I'm post what it was when corrected.

 

What I did get was an Active Code in Diagnostics:
Dash Illumination Problem
Service Vehicle
SPN 2878 FMI 4

I went to Freightliner, waited 2 hours, they said they pressed the brighter side if the toggle and it worked. They found nothing wrong. No charge. About 2 hours after sunset, suddenly my dash lights go out again. When I stop, the Active Code returns:
SPN 2878 FMI 4

I bet they cleared the code and then they worked. I'm waiting on a Nexus NL102P that I've ordered.

I can't find any info or discussion on that code.