Schematic for 02 Cadillac Seville

Does the factory plug that goes into the radio a 32-pin plug? If so then the attached diagram may help. You could replace the factory radio but some caddies have problems if the factory radio is removed, things like losing memory settings, factory alarm goes haywire, remote lock randomly stops working, etc... but the easy solution to that is relocating the factory headunit to the trunk, mine used to sit above the wheel well.