hi everyone, I am trying to put a gamma radio/cassette unit back into my 2003 golf tdi

the previous owner had an aftermarket satnav thing in its place, which he removed before selling me the car. I bought it with no radio at all so got a replacement gamma head unit as I don't really want an annoying flashing thing that'll no doubt put me off whilst driving!! so anyway I plugged the gamma unit in and there's a little red light that flashes between the TIM button and the slider thing that removes the 1-6 buttons but nothing else happens. I was expecting the display to read SAFE or something similar for me to then put the code in. some of the wiring to the connectors that go into the back of the unit have been mucked about with, would the previous person have had to cut any of the wires or something?

I'm not too hot on this sort of thing, does anyone have any ideas to help??
many thanks in advance!