Bought a 2007 Prius new. Now sometimes the dash lights (speedometer) are off. I have tried adjusting the dash dimmer and the day setting on the GPS and nothing helps until the car is turned off for a while and than the dash lights work well for a couple of months and than the lights mess up again.
You most likely have a loose or corroded connection behind the instrument cluster.
if you are handy, you could pick up a “Hayes or Chilton” repair manual for less than $25 at most auto parts stores. It will tell you how to pull the instrument cluster.
You may be lucky and just unplugging and replugging in any electrical connectors may fix your problem.
Yosemite
Good idea above. Also try exercising the dash lights dimmer control a few times, running it from all the way bright to all the way off. If that helps, an indication that the dash light dimmer control needs to be replaced. I had to replace that part on my 70’s truck a while back. Would be sort of unusual for a 2007, but anything’s possible.