I think the problem is in the steering wheel. I have taken apart the horn relay, cleaned all the connections, and in fact after reviewing the wiring schematic, when I pull what would be the gound terminal out of the relay and put test leads from the ground tab on the relay to a body ground they horns work.
Are there any ways to verify within the column the condition of the wire or in other words before buying a new horn button what I could test for?

Assuming this is a Chevelle? What year?

72 Chevelle, (that might help huh?)

The horn wire coming out of the column connector should have continuity to ground when the horn button is pressed. Your diagram should tell you the color.

Once the correct wire is found, disconnect the column connector, and use a jumper wire (to ground) to trip your horn relay. This would verify wiring through the dash harness, bulkhead connectors, and out to the relay.

If the horns blow, you know everything is good from the dash harness side of the column connector out to the horns.

To test up the column to the button you should use a meter. Resist the temptation to wire up a test light "backwards" (clip to hot, probing ground) - you could fry something. With the meter set to Ohms/Impedance, connect one meter probe to a good ground, and the other to the horn wire on the column connector. When you press the horn button the meter should go to 0.00 (from open/O.P./whatever your meter does at rest).

Thanks John, upon disassembling the steering wheel I found NO plunger, spring or little black plastic cap insert. There was nothing making contact with the ground tab you spoke of. When I grounded that tab the horns work fine.
SOoooo, now my question is does anyone have a picture, diagram or a PDF showing how these three pieces (the kit I bought has the plunger, spring and cap in it) are assembled? It might be as simple as the plunger in the spring, down through the hole in the steering wheel and the little black cap on top?

For what it's worth, this is how the '65 system goes together, they are in disassembly order, top to bottom, just click through them. This might give you an idea of what you might be missing. Sounds to me like you are missing the plunger in the cancel cam or perhaps the entire cancel cam itself. The '72 parts will look somewhat different, but the concepts are all the same.

http://heartland.chevelles.net/RCstorage/horncontact/

My horn works but is very weak sounding. Any ideas?

Sounds goofy, but give 'em each a firm whack with a block of wood.... sometimes they get "stuck" (for lack of a better term).

John, mine is much different than the one you have. It consists of a single spring to which a plunger goes down through the spring (looks like a nail, smooth with a head on it) then a black plastic cap that is notched.
I think the notch actually may play a roll in its position but I can't find this info anywhere.
I may just have to play around with it unless someone has specifics for a 72.
Thanks for the reply and the photos.
Eric