I have a spare cable that came with my ASUS motherboard a long time ago, but I don't know what is for.
It's a grey cable about 2 feet long with 3 wires that connect to a flat black 4 hole connector on either end. The white wire connects to the far end hole and has a triangle pointing to the hole
It says TYU on the black connectors and "E238099 AWM 2547 VW-1 80°C 300V 28AWG AWM I A FTI 80°C 300V ALLSAFE -LF-" along the length of the cable.
It sounds like it might be a cable to connect the sound output of a cd drive to the motherboard or sound card. Probably not useful anymore. I might be wrong, but that's the only thing I can think of which would have 3 conductors.