Mr. Haynes has the wiring diagram for the car, which you might be able to get a copy of for your car from a local library.
There are standard wiring diagrams for the various wiring formats on radios (eg ISO), and quite often a wiring loom from your local car accessory shop will have the wires labelled for the various channels, 12 volts permanent, 12 volts switched, aerial etc.
You just need to match the car wiring to the loom and Bob's your uncle.