Just went through this with my ‘41 and have it almost figured out. Here Goes… The horn is hot all the time when you push the button in the center of the steering wheel you complete the circuit by grounding the horn.
There is a hole in the bottom of the steering shaft cover just above where it clamps to the steering gear box. Its really there just filled with grease. This is where the wire comes out and proceeds to the horn. The wire runs up inside the steering shaft cover up to that little bearing at the top that keeps the shaft aligned in the center of the cover just below the steering wheel. The wire is soldered to the outside of the bearing (you will see a small indentation where it is to be soldered on). The bearing is actually hot all the time as the wire coming from the horn is hot. The bearing is insulated from both the shaft and shaft cover with a VERY thin layer of bakelite.
The rest is my best guess as I do not have all of my steering wheel parts. There is a round cone shaped cover that is suspended below the steering wheel by three prongs that extend through the 3 holes in the steering wheel hub where they somehow attach to the back of the horn button and the whole thing is pushed toward the driver by a spring inside the steering wheel hub pushing against the back of the horn button. When the horn button is pressed the round cone shaped thing contacts the hot part if the bearing and completes the circuit
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http://chevy.tocmp.com/bulletins/46csn0904.htm
