I can't say for sure, but I didn't tug at any wires and everything went smoothly installing the combi switch, which is why I figured it had something to do with it. The contacts on the wheel and column look good and when I tightened the airbag it seems to be in place. This is my first MB so I'm not sure about hearing a relay click when you hit the horn, but it isn't doing it currently.

Do horn relays go bad frequently?

I had a problem once before with the horn, but that just turned out to be a bad fuse.