Sorry I'm a bit late to the thread.
As far as I know there were at least three different styles of horn buttons/steering wheels for the X - at least here in the states.
All of the '74s I've had had this style horn button on a black 4 spoked wheel. The contact for the horn button is riveted in three places on place on the wheel.
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These had a two piece, hard, horn button that had one large diameter spring that fit over the nut that held the wheel on.
The next type had a soft horn button (safety?), of several styles. This type used two small springs held in place outboard of the nut that attaches the wheel to the shaft. On this style the contact for the horn button is attached below the nut that holds the steering wheel on. I'm not sure when these were used. Some wheels had silver painted spokes, some black.
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Here is the horn this type horn button disassembled (only one of the two small springs shown).
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The last style (that I know of) just happens to be my fav. the leather Bertone 3 spoke.
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This wheel has a self contained plastic "button that fits into the wheel. The leather cover that claps onto the 3 spokes is pressed down to activate the horn.
BTW - There were a couple of different rim coverings for the 4 spoke wheels, some in black (pic above showing two soft buttons), others in red! Not sure if there were any other colors of leather.