Just as the subject says i am trying to find out how to install an amp on the factory head unit for us tc owners. I have everything that i need and i started the project but can't seem to find a good spot for the power line to go through the firewall and i am unsure of which wires to splice to put an rca line output convertor pics much apreciated. Thanks to all who inquire.

 

I have the same problem....

 

Here's where I ran my 2 ga wire throgh the passenger side firewall. If you do a seach, I posted pics of the location.

 

I recently just did this in my tC, the wiring harness is here Scion tC FAQ Site

The power cable should go right through the gromit next to the back of the steering wheel, its not too hard to find down there, but it took me a few minutes too.