Thats what I saw , the socket would not accept a dual filament bulb, Offered when turn signals were optional?
To save anyone some time mixing and matches to find the right wire color to the rear of a truck at least the 58/59.
Likely other years are the same but it goes down the frame
YELLOW Left side to pigtail BLACK
BROWN Left side to pigtail WHITE
GREEN Right side to pigtail WHITE
BLUE Right side to pigtail BLACK
this bit of info would have saved me much time.
