I bought a new mp3 stereo recently for my 1990 station wagon and, of course, I'm looking forward to install rear speakers. Plugging my new radio, I've noticed there're rear speaker wires going somewhere inside. I took a look at the back of my car ... couldn't find them.

Does anybody have any experience with station wagons and the issue of rear speakers ? Should I do my own wiring for them or there's a way to use the factory made one ?