connecting dimmer wire on radio

I just installed an aftermarket radio (Pioneer DEH-1900MP) in my car (1990 Cadillac Deville). There is a 'Dimmer' wire left over from the car's wiring harness, but the radio does not have one. I currently don't have it connected to anything, but I need to know if there is any way I can make my radio's display brightness dim along with the rest of the dashboard illumination, like the original radio did. Should I just connect it with the 'Dashboard Illumination' wire?-Cuco

Very few aftermarket radios will dim with the dashlights.  They are usually the upper end radios.  Your radio will not allow that feature.