Please note: I will NOT be responsible if you guys destroy your vehicles! This is a "guide". I did not force you to this is. It's your own responsiblity.
Starting with the engine compartment.

Power (positive, plus, red) lead connected to the battery terminal.

The in-line fuse holder (60amp) and in the background underneath the ECU box/chip thingy, you can see the red cable, which is the power cable and it pokes through that grommet. There is a wire already through that hole, which will save you from drilling your own, plus it's close to the battery. (Thanks SiDaBa)

A closer look at the grommet/hole.

This is the view from the inside. You will see the grommet/wire underneath the glovebox compartment. So you don't really need to remove any parts just to get the wire in to the inside. (You will obviously have to when you start wiring it to the boot).

A closer look of this.

(I have skipped the bit about taking the side trims and interior parts off to wire it cleanly from the front passenger to the back.)
Well here you can see the wire has been run along the side sills bit by removing the relevant parts and it pokes back out again on the back side panel. The cable on the right-edge corner is the power cable. The rest is just the subwoofer and remote turn on cables.

Here is a shot of all the equipments placed in the boot and set-up correctly.

The reason why the amp is facing this way is 'cos my earth cable is limited by its length and the closes earth point in the boot (what I did) was behind the medic kit bit. Just carefully pull out the carpet and you should see the point. You can hook it there.

Extra this bit, a look at the subwoofer! A JBL 12" for £49.99!

Anyway this is it. Hope it helped you guys and cleared up some stuff. Feel free to ask for anything.
Catch you laters.
