Power & Ignition wires will be thicker (lower gauge) than everything else.
Also, if I remember correctly, I had to use a common ground.

Thick black wire = probably ground wire
Thick white wire = is probably +12 hot

Could you take a closer picture showing more of the wires on the car harness?

F.Y.I. -- The newer OEM radio unit's will lower & raise the antenna mast every time you eject & re-insert a CD. Also when changing between CD & AM/FM Radio. This get's annoying! Make your life easier & just hook the power antenna lead to your Ignition Wire. Then it will raise when the car is on, and lower when shut off.