here i have both cables and their connections on the opus. the smaller one shown [top] is the one i had wired in at the beginning of this thread. When plugged in, the LED would blink once, space, once...etc etc. which meant it was working properly. but it would not power up my motherboard. This one is the mystery cable.
the second cable, the bottom one in the photo [which i wired up after i was so kindly rebuked in this thread], also caused the LED to blink once, space, once...etc etc...but this one powered up the motherboard.
closeup of where the mystery cable plugs in. i have read the manual over and over and i am sure i am missing something.