If you have a speaker at the other end of the wire then you can determine which is the positive conductor with a AA or AAA battery. You will need to be able to see the woofer of the speaker.
Connect the minus terminal of the battery to one of the conductors. Tap the other conductor to the plus terminal of the battery. When you do that you will see the woofer move. If it moves out then the wires match the terminals of the battery. If it moves in then it is the reverse.