To get sufficient energy u have to connect it to the fuse box.
^ no, no you dont.
OP, please do not do this.
1) You will need to run 10 or 8 guage wire directly from the amp to the battery....depending on the amp wattage ( owners manual will likely tell you what size/guage wire to use )
2) As the other poster said, there are some areas just above or next to the brake pedal ( or where the clutch would be in the fire wall ) to push a power wire through the fire wall. I do not suggest drilling unless you can get a rubber gromet to keep the sharp metal ( resulting from the drilling ) from possibly wearing away the sheathing of the power cable. Somebody mentioned that there is a big huge rubber gasket type thing near the brake master cylinder ( when looking from inside the engine compartment ) that you can snake a power cable into the cab of the tuck and then tuck it away along the side wall near the emergency brake and then tuck in under the carpet and run it to where ever you want to mount your amp.
3) You will want to put an inline fuse inbetween the terminal at the battery and where it connect to the + terminal on the amp for extra security.
4) Please god do not even think of trying to tie the amp into your stock fuse box