Below is a rebuild of the stock Delco Remy horn from a 68 XLCH. ¹⁾
There are horn rebuild kits available, but they are pretty simple in design and a good cleaning may be all that is needed.
The repop one from J&P Cycles is on the right (3rd pic below). It has 2 wire connections as opposed to the single wire connection on the original horn.

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A bench grinder was used to grind the rivet faces off flat. You can also use a drill bit that is larger than the hole in the rivets to drill off the face.
Then you can use a center punch to knock the rivets out or pull them out of the other side with pliers.
Then separate the halves and clean up all surfaces with sand paper or a wire wheel.

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You can check the continuity of the coil but be careful not to break the wire.
Use some 400 grit sand paper to lightly resurface the contact points (you may have to push the lower contact down to get the sandpaper in and out).
After everything is cleaned up, reassemble the horn and test.
There is a small screw on the back of the horn, you can make slight turns on it to adjust the horn for the best sound.
Keep in mind that too far one way or the other and the horn will not work at all. Use pop rivets to put the horn back together after a thin coat of RTV.
Ensure that you don't get any sealant on the vibrating plate or it will not work.

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