sub install

[muj123]

I done my sub install couple days ago. Used the hole under the dash in the passenger footwell.
Installed a thick 4 gauge wire. Had to do a bit of drilling.
Now my question is what is that wire that goes through that grommet in the passenger foot well? as i have frayed the wire a little but its still intact.
just wondering what that wire is and is it easy to replace? is it a big job?
i havent noticed anything wrong with the car but still a bit worried, i was thinking maybe to split a shrink wrap through the middle and wrap it around to seal it up a little.

Also for those of you doing future installs, i know theres many guides out there but i've found some of them to be a little hard to understand.
Here is the main thing people buy is the harness and the aerial adapter.

http://www.ebay.co.uk/itm/390135210304? ... 1439.l2649
http://www.ebay.co.uk/itm/160696128367? ... 1439.l2649

the harness is very easy to work with, all you need to do is swap the red and blue wires around, which will then let your aftermarket headunit turn off when the key is out.
also, the ground. theres a guide on here where it says that a good grounding point in the rear left quarter panel in the boot. i found this to be a little vague but basically
you got to pull of the carpet on the site and you'll see a bolt which is near the light, its got wires coming of it which is a perfect grounding point. just unscrew the bolt and slip your
grounding wire in. it works perfectly.