This will sound backwards given the colors you described, but there's a lone grey wire shown in picture # 8 in the Electrical Troubleshooting Manual by the oil filter that's marked as "Not Used"...but you're saying the wire you have in that location is the Yellow/Green one?

And in picture # 14, there's a grey wire shown coming out of a loom towards the top/back/driver's-side of the power steering pump, but I can't tell if it's actually plugged into anything. You might try looking at that portion of your power steering pump to see if there's a connector with nothing plugged into it.