Ok so in my custom electrical system I am now mystified as to how the horn wiring should work. I know there are two wires in the steering column which are horn related. There is a brown cable and a brown with white stripe cable. My custom steering wheel comes with a horn button with two spade connections. I know there is a single connection via the slip ring which connects I think to the brown cable.

So the question is how does one connect the brown and brown and white cables into the horn relay circuit. I am tempted to think the earth from the relay progresses via the brown cable via the horn button then via the main body of the steering hub and out to the brown and white stripe and hence via an earth connection to earth. But what of the second connection on the horn button.....???

I am quite happy to accept that may be completely wrong....

Reality and the full story very much welcomed

Yes the ground wire completes the circuit. Earlier cars have a switch actuated by the horn pad. Later ‘72 I think have a contact ring.
The relay is activated with the ground completing the circuit.
Drove myself crazy last fall, horns not working, I could hear the relay clicking but no horn, l checked the wiring to the horns, no breaks, power and continuity. Both horns were seized. I took a hammer to them as my wife hit the horn pad and BLAR, three days searching for a break that wasn’t there, lesson learned.