Hi Colin
Does it power up at all? - Do you have the code for the stereo? Normally it will ask for the code straight away once its been disconnected from a power source so you need to make sure that the screen next to the clock is turning on and showing the word CODE.
The connectors at the back can be a bit fragile so if your screen isn't working then you'll need to unplug and try plugging them back in again.
Also the 97-98S Safranes sometimes had a cd changer in the boot so this may have affected your wiring configuration somehow.