I just copied the route of the tired harness when I did my restoration
without verifying whether it was right or not. Mine came underneath the battery box on a diagonal right to left. There's a welded on clip on the left aft bottom corner of the battery box which held it up off the gearbox cover. From there it splits, goes over the steering column, the thicker of the two branches goes out thru the firewall. I put a horn relay in mine so I can't advise regards re: the horn wiring.
Hope this helps,
Frank