So I am posting this here in the hopes that it will be easier for someone else to solve the problem I just had. It took me way more googling than I would have expected.
So, my horn would not sound even though when I pressed the horn (airbag) I was getting 11 or so Volts at the wires (13 or so if the engine was running). And when I jumped the horn directly to the battery (the horn's black grounding wire had to be connected) it would sound.
It was driving me nuts.
Finally figured out that it might be the horn relay, which is conveniently (not!) tucked behind the fuse box, under the driver side dash, on the left. You will have to remove the lower dash (easy) to get to it. Even though the relay would click and click and click when pressing the airbag, it was still bad. I swapped it out and voila, the horn works again.
Here is the best description/pictures I could find of the relay location.
It's red with 3 orangish-red wires going to it. Mine was tucked behind the fuse box and I gently pulled on the relay to get it loose and then fished it out.
Hope this helps.