When I was stationed on a ship at Pearl Harbor, I used the Navy hobby shop near military housing to do a full rebuild of the entire drivetrain for my '73 Dodge Dart; 340 small block, 727 transmission, and 8-3/4 rear end.
I also completely rewired the entire engine bay, going up a gage on all the wiring and sinking the harness under the fenders.
Anyhow, the fateful day came when everything was done and it was time to start it.
Turned the key, and instead of cranking noises, the horn beeped!
My heart sank and I hung my head over the steering wheel, wondering what I could have screwed up.
Then a sneaking thought hit me; oh, could it be this simple?
Turned the key to on, then hit the horn and VROOM, she cranked right over!
Just two wires were switched. I always thought I should have left it that way as a theft deterrent. ;P