[chumbucket]

That "white cable" on the top of your steering box is the end of your steering cable. The end of the cable looks like a flexible acme screw or worm gear that wraps around a drive gear at the back end of you tapered steering wheel post. There is usually a semi transparent (when new) tube that covers the protruding cable end to keep it clean and hold the grease.

The motor end is where your problem lies I would guess from the looks of things. Hate to say it, but it almost looks like that cable needs to come out of the tube and clean both the cable and tube, grease and re-install. I said "Hate to say it", because it's not easy to remove that cable without loosening your motor from the transom. You might get lucky though.