voyager radio not working
 

Hi, i have just bought a 2005 grand voyager 2.8crd lx(uk spec). when you turn the radio on no sound is heard from any speakers, have located the amplifier and checked the wiring i have 2x 12v batt positive and 2x batt negative and 1x 12v ignition switch feed all working. on the radio unit there is also 2x 12v batt positive and 2x batt negatives and 1x ignition switch feed all working there is also a 12v power output which is energised when you power up the radio. i have tried to check speaker cables but appear to have no continuity between front and rear(colour codes are the same) do the speaker wires go through another module somewhere? also what does the grey/yellow power output lead do as i cant find it at the amplifier end. There is also a white/purple wire which runs from radio to amplifier which is a pci bus wire. Can anyone help me with this please, i am new to this site so please go easy on me, any help will be greatly appreciated, cheers,dave.