So I've felt with a dead horn for quite a while now and just never really wanted to deal with the dealership taking $500+ just to make my horn go beep beep... I have also found that some members have had issues replacing theirs (codes thrown, fault lights). Here is my experience.
The Part:
84307-30090
2010+ 4Runner Clockspring / Spiral Cable
Yes I bought mine from eBay for $22.97 with free shipping. Yes, I assumed the risk. Does it work? As far as I can tell, Yes.
How to replace:
0. Make sure your steering wheel is at the 12 o'clock position and the wheels are straight.
1. Unplug your battery
2. Get your panel tool and pry off the covers on each side of your steering wheel column.
3. Use a torx bit to undo the screws. You won't be able to get them out due to plastic retainers.
4. Your airbag is now loose. Peel that bad boy back and use a small flat head to undo the plugs by prying up (carefully) where the arrow points down. You can remove these plugs by a little tug. The ground wire has a clip that you need to push on with your small flat head to get it undone.
5. Use a 19mm socket to remove the steering wheel retaining nut.
6. Unplug the two white clips that are plugged into the clock spring, then give your steering wheel a good tug and it should come off. If not well then you need a steering wheel removal tool.
7. Remove the bottom steering wheel shroud by first unscrewing the two Phillips head screws. Then press in the top piece on the sides and pull down on the bottom piece.
8. Remove the two plugs (black and yellow) connected on the bottom of the clockspring.
9. Remove the clockspring by depressing the clips on each side with your fingers it should remove easily.
10. Install the new clockspring ensuring the arrows are aligned on the bottom. The piece behind the clockspring has two holes that will align with two pins on the back of the clockspring. Push in and it will clip in.
11. Your new clockspring has an Orange pull pin. Pull it out.
12. Reinstall the bottom plugs
13. Reinstall the steering column shroud.
14. Reinstall steering wheel.
15. Reinstall airbag plugging in plugs and ground.
16. Screw in torx screws.
17. Replace covers.
18. Plug in battery.
19. Your horn should be back in business now and you should not have any codes thrown or fault lights.
Hopefully this helps. I'll post photos later since I didn't take any pics at the time.