To wire up your head unit you will need the following.

Perm 12v (red)
earth (brown or black)
switched 12v (yellow)

You should be able to locate the original stereo plug and this should have all 3 wires you need, if not then get in there with a multimeter and find them.

As far as the speaker wires go, pull all 8 wires up so you can reach them and then using a charged aaa type battery put one wire on the bottom of the battery and then try all the other wires in turn on the top of the battery until you here some white noise and you will have a matched pair, continue with the other 6 that are left until you have all 4 speaker wires matched and then hook them up to your speaker wires and you will be sorted.

Need any more help then give me a shout on 07730 530765

cheers

Rich