Well I got to witness the dimmer in action this afternoon, finally! I picked up my son from summer camp. On our way home a storm rolled through and of course it got fairly dark for 4:15 in the afternoon. My headlights (that I keep on Auto) came on and shortly after my dash lights dimmed. So for whatever reason the other night, it wasn't dark enough? But at 4:15 in the afternoon it was. LOL So weird.
Anyway, thanks for the input and I'm glad I know how it works now.