Actually, it's not really clear to me what you did. But maybe it's just the wine (sochu, in fact, a Korean spirit).
Easiest way is to just run current through the wire. Short the far end of the speaker cable terminals together. Now you have a loop. Then drive near end of speaker cable with + and ground (your black and red) from one RCA jack.
You can do same but using + and - active signals to drive. Or switch to voltage mode and remove short at far end.