My sleeper has two flourescent domelights. One on the ceiling and one for the dinette. Neither worked. The Kenworth dealership had tried to repair them but determined the light assembly (which includes the ballast) on both needed to be replaced. The light assemblies from Volvo are about $250 each so the shop foreman said to leave them unfunctional.
I wanted the lights to work but I wasn't paying a lot to fix them so I came up with a different solution.
I had purchased some of these LED light strips to put in the drom box. I gutted the flourescent lights and put these light strips in their place. It was a simple mod. I used two light strips in the ceiling light assembly for extra brightness.