I was just thinking back to one of these old trucks I helped out on. no horn relay till 50 something. they used to be just a hot wire to the horn and the ground was in the column. I did a quick check online and came up with this. maybe helpful.
end of the day,I havefound most "always blows" problems are in the steering column. there should be no ground there until you touch the horn contact
https://www.stovebolt.com/ubbthreads...&Number=618509