hi jenna,
I'm from US, so don't know much about a renault, however, I can let you know that they make "wiring harnesses" which you can purchase to correctly connect your stereo. It's just an adapter that snaps into the plug that was on your original radio/cassette. You just have to match up the wires from the harness to the wires coming out of your new CD player. they will be color coded so that would be easy.
If you "cut" the wires from your old stereo, the only solution is to contact Renault and ask them for a color code wiring diagram for the stereo. then you should be able to know which wires to connect to the new stereo.
Hope that helps,
sewellp@yahoo.com
Patrick Sewell
February 2008