The spare tire key/lock on Ford trucks and SUVs is not the same a wheel locks.
This is a very common problem -- Ford's spare tire key being missing in a used truck, van or SUV. Ford has discontinued this spare lock model, because it obviously sucks. Unfortunately, this means your dealership probably can't order the new spare key for you. The company that made them is still around, and you can find out what size it is and re-order, but this is not the best solution.
Here is the best answer I found, for what it's worth.
Remove the spare tire lock completely, and you don't need a key at all. Problem solved. You must first remove the black plastic guide that leads to the spare lock. Then, with a screwdriver push our the lock, or you can pull it out with pliers. Afterwards and forevermore, you can use the black rod extension to turn the spare tire winch mechanism, and it will work beautifully every time.
If you want to read more details about how to remove the lock, and pictures to guide you, check here: http://www.ford-trucks.com/forums/333925-used-truck-has-no-spare-tire-key-2.html
Also, if you don't want to drive around with your spare unlocked (because, apparently, people steal spare tires), you can get an aftermarket tire lock for a very reasonable price -- and it will work, and be a heck of a lot better than the stock spare lock/key discontinued nightmare.