Hard-wiring power behind the dash

The Prius doesn't use anything *like* colors you'd consider standard.
Go to Techinfo and buy/download yourself an Electrical Wiring Diagram
[EWD] and the companion to it, "location of parts". Ground in this
car is often white with a black stripe but not always; positives can
be black [yeah, go figure] or red or light green or anything. You'll
find places where two identical white wires come into an ECU plug
right next to each other from two different sensors -- how they
figured *that* one out while constructing the harness I'll never
know. Basically if you don't identify exactly what wire you're
after and what hole in which plug it goes to, you're flying
completely blind and are likely to get nothing but smoke for your
efforts.
.
That said, if you describe what type of power you're looking for
[constant, switched, what ignition state you want it switched in]
and expected current levels, some of us might be able to look up
some things and make recommendations. For example, I take accessory
power off that same positive to the front "lighter" style outlet
but over at the main inside fuse block by the driver's left knee
and by tapping a light-green wire, before it routes through other
things and turns into the black wire at the outlet. And I know
which fuse feeds it.
.
_H*

 

You may want to go to http://www.evnut.com/prius_12v_outlets.htm to see one way to do it.