There are two harnesses available for an '05. The LX does not have the extra amp switch wire. The LX-Sport (leather steering wheel and amp), and EX needs the extra wire. The Red should be a switched wire (turns on/off with the car), the Yellow should be constant 12v.
If the vehicle side of the harness has a solid blue, or a blue/white wire, you will use the blue/white wire from the radio side to power it up. Pick up a cheap voltmeter and test the output power of the wires from each side to see what is what.
'05 Sorento LX 4x4. Purchased 9-14-11 43,800mi. "Karinka"
'08 Spectra EX 5speed. Purchased 3-25-12 43,500mi. "Saki"
'99 Sephia 5speed "Kurumi". Traded in 2006.