Classic/Antique Car Repair: horn switch wont make horns sound, bosch relay, pontiac catalina

Question
QUESTION: The horns on my 1968 Pontiac Catalina do not sound when I press the horn button on the steering column, but they do sound if I touch a 12V lead to their ungrounded terminal.
There does not seem to be any continuity between the small wire connector under the horn button and any of the wires that go to what I believe is the horn relay. The original horn relay in my car has apparently been replaced with a Bosch relay that's different from the one described in a previous answer. The Bosch relay in my car has 5 terminals, none of which is labeled "S" or "H" or "B". The leads to this Bosch relay may in fact be connected to the wrong relay terminals, and I'm not sure how it should be hooked up. As I wrote, none of the leads at the Bosch relay show continuity to the horn switch connector that's under the horn button at the center of the steering wheel.
I'd like to add a new wire from that small wire connector under the horn button to one of the horn relay terminals, but I cannot see where the wire from that small connector exits the steering column. I thought if I could find where this horn switch connector lead exits the steering column, I could splice in a wire there to connect it to one of the Bosch relay leads.
Can you tell me where I can find the wire from the small lead under the horn button as it exits the steering column? It's not clear to me from a previous answer I got whether the lead in question exits the steering column under the dashboard or on the engine side of the firewall.

ANSWER: That wire comes down the column with the directional signal wires and exits the column just behind the dash. The wire color should be black.
Brad

---------- FOLLOW-UP ----------

QUESTION: Thanks, but does "just behind the dash" mean under the dashboard on the passenger side of the firewall, or under the hood on the engine side of the firewall?

Ron

Answer
A bunch of wires comes down the steering column and exits the column just under the dash near the brake pedal. There should be a black wire in there and that should be the one that goes to the horn switch and completes the circuit to ground when the horn button is pressed.
Brad