Wiring.

Would anyone have some sort of wiring or help me out in sorting this problem ?,I managed to get one of these alternative sat navs/gps etc etc head unit but when I plugged it to the Skoda harness it only worked with the ignition on and produced no sound whatsoever.Are cars with the genuine amp and extra speakers and audience head unit wired differently to those with the standard stream with eight speakers ?,my mate fitted the same unit in his octy which is equipped with the latter and he had sound working,so he told me .... Anyone ever encountered any problems ?.