1. Everybody's cluster dims in the heat as it gets old.
2. There's no flicker when brightness is full because the lights are flickering brighter, not dimmer. Mine does the same thing, could be the adjustment control. But I still have DRLs. Replacement headlights, but they have DRLs. If I figure it out, I'll post.
Why do people insist on turning those off? It's illegal, and much safer to have them on. Something about VW drivers wanting lights off, while other drivers are turning on all kinds of lights on the daytime........ I'm beginning to thinmk the latest gen Mustangs have no off switch for the fogs.