Passat horn...

horn, fuses, wiring, steering column spiral spring, horn contacts. a good place to start is check the fuse!

And ground wires. The horn button on the steering wheel is usually a switched ground (instead of 12V+). The horn essentially has 12V all the time the ignition is on but makes noise when the horn is pressed on the wheel which essentially "connects" the ground circuit to chassis ground.

To further clarify, the horn itself probably has two wires. With the ignition on, one should test out at 12V+ (more or less). if it does, the ground is probably bad. With someone pressing on the horn button, measure continuity between the ground wire and ground and you should get it. If not, the ground is bad. if you do, the horn is bad. You can also just jump the ground terminal on the horn itself to ground w/the ignition on and the horn should sound. If not, it's bad.