Remove the steering wheel centre you will see the old wire and a rubber plug.
Remove the plug and pull the wire.
Next get a length of steel wire and feed it through the steering column from the engine compartment. When you see the wire the wire coming through the steering wheel, your there.
Attach your new horn wire to the steel wire in the engine compartment and pull it through the column.
Cut the wire to size and solder the cable shoes to the wire.
Connect the wire, place the rubber plug and steering wheel center.
Don’t forget to insulate the cable shoes inside the steering column your neighbours will appreciate that.