VW Gamma radio problems

Hi
 
I bought a vw gamma radio and cd head unit to put into my MK4 Golf.  I previously had a Alpine head unit and changer in there which i have taken out.
 
When I connected the VW radio head unit to the car, nothing happened.  It was like there was no power to the radio.
 
I was expecting to see the SAFE mode display so i could enter the code but i can't get any display at all.  I thought it may be the stereo but then i tried connecting it to a polo and the red LED flashes but still no display.
 
I am wondering if the wiring on the stereos differ at all and thats what the problem may be?
 
Anybody have any ideas???? Please help.
 
Thanks
 
Hiran

i have had a look in the car and the wires on the iso connectors differ from the number of pins on the back of the head unit.
 
there are 3 wires spare wires in the car which are not plugged into the black iso connector. They are:
 
red/white
blue/white
grey/white
 
the 3 missing wires on the unit are:
 
MUTE
GA
K BUS
 
do these coloured wires sorrespond to those pins and if so which colour is which!!!!!!!!!!!!???
and help would be greatly appreciated.
 
Thanks
 
Hiran