2000 sunfire stereo

Are you using a harness?  You may have to run an accessory power to the fuse box, I think that that vehicle uses the 70-2003 harness(metra) and would require you to run your own accessory wire.  If you are kind of iffy about the ground just hook it directly to the vehicle chassis and that will fix your ground problem. 

As far as not knowing what to do with the switched 12v wire...hook it to the red wire on your sony deck.  Make sure you test that wire with a DMM and read the voltage when you have the lights on and off.  If the voltage drops when you turn the lights off then you have the illumination wire and I recommend you running your own accy wire.  FUSE IT with at 10 amp fuse.

There's really no need to relocate the factory radio in the sunfire....especially since it's only a 2000.  I would use a harness...it makes things soo much easier.  It DOES take the 70-2003 harness and if I remember correctly, it MAY have voltage at the acc lead from the harness....some do, some don't.  Chimes are annoying and if RAP doesn't matter to you, you can run a fused acc lead to the ignition harness or the fusebox.  If you don't go to the ignition harness, I would suggest using a 12v boost relay using some switched ignition point in the fusebox or better yet, at the A/C control switch.  In case you aren't sure...the 12v boost relay is as follows: 85 - Input(switched 12v from vehicle)  87 - 12v Constant  86 - Ground  30 - Acc output to deck