im pretty sure there were 2 yellow wires but not on the same plug
you should be using the plug that connects to the top left of the tachometer
you can always just do a test cut, get a pair of wire strippers and strip a small section on the one yellow wire, count over from one end and whichever has the yellow wire coming up as the 10th position attach the power wire from the shift light...if it comes on bingo, if not try the other...be careful though