Where to tap a wire under the hood?

Find your location here;

Toyota Prius (XW30) (2009-2015) Fuse Diagram • FuseCheck.com

I would use a fuse tap adapter like one of these;

 

You don't even need to tap an existing fuse or wire. The Gen 3 has two open terminals at the rear of the engine fuse box that have constant 12v DC. All you need is a wire terminated with a push on terminal.

https://priuschat.com/index.php?posts/2450066

Posted via the PriusChat mobile app.

 

As was pointed out in that other thread, those two locations are unfused, so whatever circuit you push on there had better have a fuse of its own.

 

Here's how to access the main incoming 12 volt point, on the under-hood fuse box. It's a ring style connector. Any yeah, good to have an inline fuse, on whatever you add: