Two problems related to back up lights have been reported for the 2007 Toyota Prius. The most recently reported issues are listed below.
The plastic weld process or other type of gluing process used to make the vehicles exterior front and rear turn signal, brake and back up light lense assemblies or housings fails. All four, two front and two rear, exterior combination light lense assemblies suffer this premature and serious failure. When these exterior lenses begin to fail they allow water intrusion from the exterior of the vehicle. This allows moisture to penetrate into areas of the lense assembly which support all of the light bulbs used to warn or signal other drivers or pedestrians. At a very minimum this problem results in premature bulb failure for all of the signaling systems specified above. Researching your site this problem has been reported to you many times and Toyota motor corp. Is also aware of this problem. What you don't seem to be aware of is the most serious concern resulting from this problem; if the right (passenger side) rear lense suffers this problem and begins leaking, the water runs or drains directly into the interior 12vdc starter battery well. This battery well is as deep, or deeper than the factory installed 12vdc starter battery is tall and can result in water overtopping the battery. This causes shorting/grounding across the positive/negative 12vdc starter battery terminals. This prevents the operator from starting the vehicle and cuts off power to all 12vdc electrical systems including emergency flashers. It could easily result in serious damage to the 12vdc starter battery and many expensive 12vdc electronic components or systems. This problem is more serious in areas that receive high amounts of rainfall. I called a Toyota authorized dealership, lum's auto center, and reported my car wouldn't start. They suggested I bring it in. After 4 days they were unable to find the problem. No diagnostic codes were logged. This is a serious problem needing immediate attention!.
During cold weather I lose all odometer speedometer backup light gas gauge . Back up lights have caused a lot of close call when I'm backing up one time I got close to hitting a pedestrian because they did not know I was baking up I have ran out of fuel on the freeway and I never know how fast I'm going. This problem is well documented and Toyota knows a bout the problem but will not issue a recall.