I have a 55 2nd series 6400 with the round lights on the fender.
Looking thru the shop manual wiring schematic, there is NO turn signal, just stop signals.
The signal on the steering column does look like it was added afterwards.
Was thinking of doing away with turn signals, like the cool Harleys - just use hand signals. The thing is, instead of 500-700 lbs between me and the next car, I have 7500 lbs!!!