Local libraries often have Haynes manuals. You'd probably find a wiring diagram in there.
However, working out which wires are which is fairly easy if you've got a multimeter. (�5.99 from Maplins. Even cheaper from some discount stores. Nothing if you borrow one from a mate):
Switch the multimeter to a suitable DC range for the car's battery. (This is typically the '50VDC' range). Touch the black probe against any bare metal on the car's chassis. Then, with the key out of the ignition, touch the red probe against each mystery lead in turn. The one which moves the meter is the 'permanent live' . Label it (and remember not to touch it while you're also touching the chassis -it could be painful!).
Turn the ignition key to the first position and repeat the process. When you find a lead which moves the needle, you've located the 'switched live'.
Now switch the meter to the resistance position. Still with the black probe touching bare chassis metal, try the other probe against each lead in turn. The one that moves the needle the whole way across the scale is the earth lead. (Some wiring systems have separate 'earth' and 'negative' leads. If so, both leads will move the needle fully across the scale. To distinguish between them, disconnect the battery's negative terminal. The only lead that now moves the needle is 'earth'. The one which has stopped doing so is 'negative).
Now take a 1.5V torch battery and keep trying various pairs of leads connected across it. Eventually, you'll hear a click coming from a speaker every time you connect a certain pair of leads across the battery. You've now identified the two leads which feed that speaker. Repeat until you've identified all of the speakers.
Chris