You should find that the speaker wires will be in pairs - usually each pair will be the same colour but with one wire in the pair having a 'tracer' marker along it's length. To find out which speaker is connected to which wire, get a 1.5volt battery and touch the bare ends of each pair of wires to each end of the battery.You will hear a slight 'thump' from whichever speaker the wire is connected to. Don't leave the battery connected! You only need to touch the wires briefly to get the speaker cone to move. Mark the wires with a sticker or note the colours on a notepad.
The power wires could be slightly more tricky. Usually there will be three power connections. One is a permanent 12volt feed (you can test this with a multi-meter or bulb), one is a SWITCHED 12volt connection that only has 12 volts on it when the ignition is ON, and the third is ground (0 Volts). A permanent feed is USUALLY coloured red, but i have seen ground wires AND switched 12 volt wires coloured black, so be careful. Test them with a multi-meter BEFORE connecting them to your stereo as you will do irreparable damage to your stereo if you get it wrong. There is no problem connecting the stereo to the permanent 12volt supply, it just means that you have to remember to turn the stereo off when you leave the car.
The only other wires from the car would be if you have an electric aerial which will be a single wire, and obviously the aerial lead itself.
Hope this helps.
Karl., August 2007