There is one common harness for the driver's side airbag, audio controls, cruise controls, and horn. (The Z2 harness, to be specific.) See page
EL-30 in the FSM. To get at this, see the steps involved starting at
RS-17. You'll need a steering wheel puller and some tamper resistant torx bits to do it. Check every harness as you dig deeper... there's four or five of them, refer to the electrical schematic on EL-30.
With my Pathy, I've only gone as far as doing work with my combination switch, so I never went as far as pulling off my steering wheel to get at that "spiral cable" connector behind the wheel. I've done it on other vehicles though... a bit intimidating the first time, and my first drive afterwards I'm always a bit nervous.

Two tips -- take lots of pictures at each step, and before you remove the steering wheel, make a pair of marks (on the wheel and on the base) so you can match them up when re-attaching the wheel. (I didn't see this step in the Pathy/QX4 service manual, but it's something I've always done.)
Edit: Bonus third tip, always assume the air bag will go off at any moment. Treat it like a bomb. Unplug it before you start any work (usually a yellow harness or wire, I'm sure it says how to unplug it on RS-17 or just after), and then take it right out of the vehicle and put it somewhere safe, like a workbench. Make sure it's oriented so that if it does somehow manage to deploy, it won't fly around and cause damage. I've been in an accident, and the air bag probably helped a lot, but those things still cause trauma like you wouldn't believe. My chest was purple and I had hairline rib fractures, PLUS the deep, deep bruises to my shoulder and hip from the seat belt. I wouldn't want to be working on the Pathy and all of the sudden have that sucker go off in my face.
There could be other causes for this failure, but if all the fuses are OK and this harness controls all the systems affected, then it's where I'd start.