On later 70's VWs the brown (horn +12V return) came into the steering going through another type of slip ring which is insulated from the column, up to the button top. The chassi/common/ground came up through the column itself, which had a wire jumper across the coupling you show. Didn't need all the black rubber as electrical insulators but as cushions, but allowed an electrician to recreate the old style (+12V column) easily I think if desired.
Just a few clarifications on the horns with a relay. The horn is already grounded and is supplied power from the relay only when the relay is "on". The relay has the 12V but no ground until the horn button is pressed to complete the circuit. In other words, the horn button is turning ONLY the relay on and off. That's why it's there. No part of the horn circuit flows through the steering column, just the relay circuit.
