fitting a sony radio to a saxo vtr w reg?

I've bought a saxo vtr w reg. The wiring is a bit confusing. From what I can see the four green wires are speakers and same with the four reds. So that leaves me with four more wires, two grey one thin and the other thick, a blue and a yellow. I think I have to put the two grey ones together and wire them up to the yellow and red one on the radio but what do I do with the other two the yellow and the blue? Can some one please help me thanx.