If you are installing a new amplifier or doing any other electrical work, you might have to run power wires from the engine compartment to the cabin. There are several ways to do this: using existing pathways on the driver's side, running the wires along the fender etc.
Another way is through a rubber grommet located on the passenger side of the firewall behind the strut tower. Use any tool with a pointy tip to remove this grommet.



Poke some holes into the grommet and run the wires.
Inside the cabin remove the glove box door and the tray under the fan assembly. The wires are gonna come out at the location shown in the picture or you might also decide to poke a hole into the insulating material.



In my case i hardwired a power inverter to the battery.

 

this is pretty nice, good write up.

 

+1 good write up.

 

the location of the inverter is perfect for a road trip where a passenger might have a laptop . I myself use cigarette lighter inverters but the ones straight to the battery provide more power.