I think I am beginning to do an about face on this, I think both the lights in the 250 chrome side housing are sidelights/parking lamps. I think the 4A had flashers on the side, I think with the federal legislation effecitive January 1, 1968 the side flasher was converted to a side light on the 250, the federal legislation required lights or reflectors on the sides, red in back, amber in front to make the car visable and indicate the direction of travel on cars sold new in the usa.
This is consistent with the period wiring diagrams I can see for the car as best I can read them and consistent with the two red wires coming out of the believed to be original side flasher on my 250. As I mentioned earlier I have other side flashers with one red and one green and xxxx wire (ignoring the black ground wire which doesn't add to the discussion here)
That being said I wired mine to flash, and I guess just to muddy the waters I have the original equimpment flasher, and with just the fronts in the grill and rears wired I get a very fast flash, when I wire up the sidelights into the mix the flash is the slow and steady I equate with working right under the proper load, so who knows??