TeamSwift

The easiest way to be sure what the wires do, is check them with a multimeter or a test light before you wire them up.

Connect one lead to something grounded (like the metal brace under the dash) and the other lead to one of the wires:
• if you get a voltage reading with the ignition in the OFF position, the wire goes straight to the battery
• if you get a voltage reading with the ignition in the ACC position, the wire gets power from Accessory (it will probably also get power from ON as well)
• if you get a voltage reading with the ignition in the ON position, the wire gets power from Ignition/On (check if ACC delivers power too)
• if you don't get any voltage reading from the ignition in any position, turn the lights on to see if it's on a lamp circuit. You should see a voltage fluctuation if you turn the dimmer knob
• if you still don't get any voltage reading from the ignition in any position, trying doing a continuity test to see if it's a ground wire.
• you may also have a factory speaker wire on hand, don't bother trying to test for this, factory speaker wires should be replaced when you install a stereo anyways.