OK, I'm surprised no one has mentioned this yet.....do you have factory keyless entry? (Remote to lock and unlock your doors) I know it doesn't sound relevant but if you do then I would not do this install yourself and let a professional do it to save you the headache.
The factory keyless entry system is built into the factory deck and you actually have to keep it plugged in and have to hide it behind the dash for your keyless entry to still work. AGAIN: you will have to hide your factory radio behind the dash! I hate doing these cars for that reason and I highly recommend having someone else doing it to save you time and a headache.
If you do not have factory keyless then to keep your domelight working after adding an aftermarket deck you need to connect the light green/black wire to the light green/red wire. I believe they are in a green plug.