1. Disconnect the negative battery terminal and make sure the front wheels are straight ahead.
2. Pull the front of the steering wheel off. It's just a friction fit and you have to pull pretty hard. The horn wire is attached to the back of the steering wheel and should just pop off.
3. Next you'll need a 27mm socket on a 5" extension to remove the nut you see in the above picture. Don't use the wheel lock as opposite force when loosening or tightening the nut. Get a helper to hold the wheel tight for you. Also, orient yourself outside of the car or at least so that the direction you're pulling on the torque wrench is away from the windshield to avoid breaking it. Loosen the nut most of the way but leave it on while you pull the steering wheel loose so it won't hit you in the face. Once it pops loose take the nut the rest of the way off and remove the wheel, nut, and washer.
4. Turn the steering wheel upside down and take out the 3 screws seen in this picture.
You'll be left with this piece which you will transfer to the Momo hub adapter.
5. But first you have to switch out the stock wire with the one supplied with the new hub. The connector at the end of the stock wire is too small to fit onto the tab on the Momo hub. You could just cut it off and splice the new one on but I wanted to be able to switch it back someday. You can also do what I did in this picture and just add the new wire to the end of the stock one but be sure to tape over the center connection because if that touches any metal the horn will sound continuously. I actually bent up the 5 brass tabs, removed the wire assembly from the plastic part, and switched out the stock wire for the new one.
6. Now feed the wire through the hole in the Momo hub and reinstall the piece with the 3 screws you took out.
It will look like this (the screws aren't installed yet in this picture).
Now attach the hub to the wheel with the 6 supplied allen head screws.
7. Reinstall the wheel tightening the 27mm nut to 40ft-lbs. You'll need a second pair of hands or a dowel of some kind to keep the steering wheel from turning while you do this.
8. Install the retaining ring onto the back of the new horn button, attach the wire to the back of the new horn button, and pop the button on. You're done!
If anyone has any other tips to add feel free to chime in. I'm not sure how to get this added to the DIY thread. Maybe one of the moderators can help with that.