Recently I have noticed that then I turn on my headlights, the dash lights and display dim very noticably. I have an '04 Prius with about 73,000 miles on it and haven't noticed such a difference in the brightness of the dash light and display before. Is this an indicator that my 12 volt battery may be on the way out?
No, it's an indicator that the scroll wheel that sets the dash brightness has been changed.
The dash lights assume that it's dark out when you turn the headlights on. Adjust the little thumbwheel and they will brighten up again.
It's an indicator that you've moved the dash light dimmer.
You know, so many people don't actually DRIVE their cars. Those people are simply passengers who happen to be in the driver's seat, steering the wheel. But knowing about their cars and how their cars behave? That's too hard...