You won't get any pushback from the cops since you aren't legally required to have a third brake light in the first place. You aren't even required to have brake lights on each side of your truck, either.
Your truck left the factory with one tail light/brake light on the left hand side. There is no law requiring antique vehicles to be modified in order to meet present day standards.
As for your switch, test it. New parts today are generally junk from China and may or may not work at all straight out of the box.
1950 Chevrolet 3100 (Ol' Roy)
1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)
