First off take the card off and see if there is any speaker wires there, some of them have the wires installed and ready others dont.
If the card has the markings for a speaker to be fitted, then its simply use some self tappers and screw it into the plastic, use the old wires if they're there.
IF there is no wires there then you have 2 options.
1) install new wires and route them through the car to the back of headunit, strip the connections block down and plug in 4 new wires for a connection to the HU.
You not actually be stripping down the block, just finding the already installed wires and putting 4 new ones in. Ball ache though.
2) If you have an aftermarket HU, buy a small amp, some thing like this,
http://www.caraudiodirect.co.uk/alpine-pmx-f640.html fit it under the passenger seat, dont worry about screwing it down, use the velco grip on the underside of the amp (NOT COVERING VENTS). A small power wire like 6-8awg will be enough. Run from the battery to a fuse and then through to the amp via the grommit for the bonnet cable. Earth the amp to a metal bracket for the seat or near the hand brake.
RCA's from the HU to the amp and hey presto.
Also being amped the speakers will be alot more powerful.
Dont buy an amp install kit either, they'll be s**t unless you pay a healthy sum for one.
Power wire - buy 3 mtr's of
http://www.caraudiodirect.co.uk/gro-gzpc10r-ground-zero-gzpc10r-red-cca-8awg.html
Remote - 3 mtrs
http://www.caraudiodirect.co.uk/celsus-amp-remote-cable.html
Fuse holder - 1 part
http://www.caraudiodirect.co.uk/raptor-gfbw2-agu-fuse-holder.html
Fuse - 1 part
http://www.caraudiodirect.co.uk/vibe-agu30-fuses.html
Wire terms -
http://www.caraudiodirect.co.uk/phonocar-ring-terminals-8awg.html
RCA's
http://www.caraudiodirect.co.uk/phonocar-4-262-double-shielded.html
Speaker wire - 4 mtrs of.
http://www.caraudiodirect.co.uk/connects2-ctsw318-speaker-cable.html
All that with delivery comes to £18.66 and its all you will need. The next best amp kit is £18 and that dont come with speaker cable or terminals.
Caraudio centre will be about £20 and Halfrauds about £30 both without the speaker cable or terms.
