Is there a (temporary) wire keeper on the switch itself?
IIRC, there should be small piece of paper, like what we oft find in a fortune cookie...if it's not hiding down inside the box, maybe someone's been in there before.
See:
http://www.mustangandfords.com/how-to/engine/5657/ - note the shipping wire that keeps it in the right place for install. Have the key cylinder in the 'off' position. When the rod/pin in the column, and the switch guts are both in the right position, bolt that sucker down. Don't force it. If it doesn't act properly when tested, take it back out and verify indexing.
Do you have the correct torx bit? Security T-27, I think. See that link for details.