I swear I read somewhere that they came from the factory with speaker wire already run.
??
That would be interesting to read.
My 54/55 GMC COE, that had only worked in an orchard all its life, had no radio speaker wiring. Almost everything in the interior (except for switch for the 2-speed rear) was original. No radio.
I now have an original 6v and a 12v GMC radio, one of which might end up in it (unless I use a modern clone radio).