All you need is a 12v circuit tester to work out the wires coming out of your dashboard (permanent live, switch live, earth) and then just download the manual for your headunit and that will tell you what wires are what.

The only slight hassle you might have is working out which speaker wires coming out of the dash go to which on your headunit but you can soon work it out... just use your fader and balance control on the headunit to work it out and if you connect a speaker positive and earth the wrong way round you will hear the difference!! ie less bass!!

hope this helps.