We either skipped over, or thought you knew, or maybe misled you.
The horn should have a relay.
So the relay has three terminals. I don't know if you have a relay yet or not, don't know if your wire colors are correct,
but the normal is:
1. Old school relay terminals were marked "S" GRN to switch/horn button, "H" BLK to horn hot terminal,"B" Red to fused battery hot. (always hot type).
2. New school relays are marked 1, 3, 5.........1 is horn hot terminal, 3 is BAT hot supply and 5 is horn button wire.
3. Modern is a Bosch 4 pin relay. Normally open. pins 86 and 30 wired to battery hot. 87 to horn hot. 85 to horn button.
4. The horn body is still grounded to chassis for all relay types.
Relay
