My Jeep had no rear speakers, and no wires in the hatch for them. However, there were wires for the rear window wiper, sprayer motor, and for the rear defrost, none of which my Jeep has.
I found the speaker wires coming from the radio behind the cover in the cargo area behind where the spare tire would sit. I used a multi meter to determine that they were indeed the speaker wires.
Then I traced the unused wires in the rear hatch door back to where they were connected, right by the speaker wires. I then just cut the unused wires, and then spliced them into the wires going into the hatch, wherein I was then able to splice them into my new, $20 Walmart speakers I was installing. Worked great, and I did not have to pull any new wire.