For most radio's that I wired up yellow goes to a constant hot and red goes to a hot when the ignition is on. On mine I just have red and yellow going to a constant hot and the radio can play all the time and the clock stays on. It's up to you. If you google radio wiring guide there will be easy pictures that will help you out emensly.
http://www.siocommunications.co.uk/W...dio_wiring.jpg