detailed wiring schematic?

He all, I recently got the prius c 2016, loving it, but I'm ready to add some things to it. I also like to use as much of the existing wiring as I can. I'm currently looking to add a secondary horn that requires about 20A. Looking through the fuse box in the cabin, I noted that there is a 25A fuse for the moon roof. However, my model doesn't have a moon roof, so essentially this circuit is free and I would like to use it. My only problem is I don't know which wire (or pin) coming from the fuse box will link me to it (or even if there is something else on said circuit).

I've done quiet a bit of digging but i have yet to find a detailed wiring schematic for this car, any help?

Worst case, is there an easy way to find the pin? I assume I could use a continuity tester to find it, but I'd rather get the info from the schematic.

cheers!

 

I'm well aware of that. in fact, due to it's loudness, I'm actually having a separate button to operate and preserving the original horn and it's wiring. The main reason i'm wiring into the moon roof circuit is simply so that it's a cleaner instaallation, just a preference really.