From your pictures of the speaker wire with bare wire on one end and rca in the other. how do you know which wire is + center and - shield? They doesnt seem to be marked. Or maybe +,- is not important for this mono rca?It would go to the speaker outputs of a receiver.
Red on the receiver goes to the center of the RCA jack on the speaker, black to the outside part.
Buy a couple of RCA plugs from Radio Sacked or Best Buy or Big Lots and solder some speaker wires to them, and connect the other end to the receiver, then plug the RCA into the speaker.
Or buy like this: