I'd like to see the shot. The only pic I can find of a yellow open platform coach on the San Juan is a RWR shot of the train at Osier in the summer. It appears no one bothered to take a pic of the last westbound San Juan with the made up consist.
There are pics in NG Pictorial Vol II on pg 68 that show interiors of 280 and 284. the 280 shot has 3 lamps circa 1940, the shot of 284 (you can read the end # above the door) taken in 1950 shows no signs of electric lights. but shows a keresene ceiling fixture. There is also a shot of the interior of 320 without lights or any signs of kerosene lamp vents. The last time I looked noticed the inside of a San Juan coach, they still had interior light fixtures as well as light fixtures in the vestibules.