Don't let the very comprehensive and confusing "by the book" directions TXFRDOwner posted scare you. IT IS EASY. Follow the directions below.
1. Purchase the correct passenger dash air bag cover from an online dealer. I paid about $100 plus shipping, and was able to specify camel color for my interior. It doesn't match perfectly since the original interior has faded a little over time. However, only I notice it.
2. Move your passenger seat all the way to the rear position.
3. Disconnect the battery and wait 30 minutes. Some say just the negative, some say just the positive. Just disconnect both, and tie them back so they don't bend back and touch the battery posts when you aren't looking.
4. Lower the glove box and push in on the 2 side walls to allow the door to hinge all the way to the floor.
5. Search and watch a few of the videos on U-tube that show how to remove the passenger air bag from the dash of your Ford Expedition. The videos do not really show you how to remove the air bag cover, but they will show you which screws to remove. There are 8, they are easy. Took me a few minutes, longer to round up the tools than to remove the screws.
6. Use a pry bar to pry the top left/right and lower left/right sides of the air bag cover away from the vehicle. Use a plastic pry bar if you don't want to scratch your interior. use a screw driver if you don't give a shit.
7. Pop the entire assembly out, let it kinda rest half out of the hole, reach in and disconnect the connector for the air bag. Pull the assembly out of the vehicle.
8. Remembering the top/bottom of the cover on the air bag, Place the air bag cover (with air bag attached) onto the garage floor and work the 8 clips out of the holes on the cover. This is easy, just pry one side, the other side falls right out.
9. Put the new cover onto the air bag. Do this by putting the air bag clips into the holes on the new cover.
10. Slide the new cover and air bag into the vehicle. Pushing (or hitting with your palm) the top left/right and bottom left/right to pop in the holding clips on the new cover.
11. when you have the new cover sitting flush like the old cover did, screw in the 8 screws.
12. bring the glove box up, push in the side to allow the glove box to close. Open the glove box to make sure it works.
13. Gather your tools, get all your install junk off the passenger seat.
14. Connect the battery back. If the air bag doesn't deploy, you did a good job.
15. Move your passenger seat back to normal position. OR let your passenger worry about that.
Took me about 30 minutes. I literally spent days researching this because everyone makes it sound like you are dealing with a live grenade someone just threw to you. You are, but once you disconnect the battery and then the connector, there is no voltage to trigger the air bag. If there was, there is no garage that would deal with these things.