Ok, here it goes from the ETM (do a search and download the one for your car is it is very helpful!):
1- red/white (yellow on factory radio) wire is hot at all times, however the best way to do this is to put two new wires through the firewall and connect them to the auxiliary fuse block just outside the main fuse box. One is hot at all times and the other is switched. By doing this your radio won't die every time you step on the brakes (fuse 5 has a lot of circuits on it).
2- gray/red (white on factory radio) is the input from the dashboard light switch.
3- purple/white (purple/gray on factory radio) is the switched power wire. See comment in number 1 above.
4- white is antenna on wire.
Do not reuse the speaker wires as it has a common ground! Install new speaker wire for all 4 speaker locations!