Maybe the original depended on a chassis ground, and the replacement uses a wire instead to a remote ground. If that's the case, a wire would be preferred. Especially if you can attach it to the main chassis.
Does your new switch have more functions than the old? Do the colors match up? You may need to use a multimeter to beep out the wires and switches. Or did the new switch come with a wiring diagram? If the colors don't match up, it would be a good idea to cross reference the new switches wiring/colors to a factory wiring schematic. They are available for download on this site.