One problem related to trunk wiring has been reported for the 2006 Toyota Prius. The most recently reported issues are listed below.
Hid headlights go out randomly while driving. Each one goes out separately, but sometimes they will both happen to be out at the same time. While driving, this is corrected by turning headlights off and then back on. Same thing happens with the yellow running lights, one may turn off randomly. This began happening in fall of 2011, however new bulbs (hid and running lights) were purchased and the problem stopped temporarily, but within 1 year the same problems are occurring again. Similar problem with the rear license plate lights; one will be off randomly, but shutting the trunk hard seems to appease the problem. This may be a wiring problem, but the front lights should not be turning off randomly.