It already is on a switch (ignition)... now you are just going to make it to be on 2 switches. That will be fine if you are only going to use it when the key is on. Otherwise, just pull the headunit, run a fused +12 from the battery or another source, run it through your switch, then remove the fuse from the kickpanel for the radio and run the +12 from the other end of your switch to the 12+ wire that turns on your headunit (just plug it into the harness). If you do it, do as clean a job as possible, do not cut or do anything you can't easily undo before you sell your car.