SRS module and Multi function steering wheel

Multiple dead circuits all related to the steering wheel typically have one thing in common. That is the clock spring. That's a wound-up ribbon cable in a plastic housing right under the steering wheel. It's common for that ribbon cable to break.

Normally, based on the symptoms, I just replace the clock spring without doing any tests because it is so common. There are two different electronic systems that can be used. Typically the horn, cruise control, and air bag use individual circuits. As the ribbon cable starts to break, one of those circuits will fail first. Most people notice the "Air Bag" light turn on or the cruise control stops working. That is followed by a failure of the second system days or weeks later when the ribbon cable breaks further.

With the other, less-common system, all the circuits share a few wires in the ribbon cable. Each button produces a different voltage signal so a computer can figure out which button you're pressing. When a wire breaks, all the systems will fail at the same time including radio controls and anything else on the steering wheel. Typically the air bag initiator circuit will still have its own wires and if those haven't broken yet the air bag light won't be on.