Today I was watching a video about ATSF in Southern California and saw that on most of the second generation diesel locomotives the upper headlights were covered and only the lower headlights were on. I have a number of ATSF second generation diesels on my layout but I never paid attention to the correctness of the headlight positioning; I run them as they came. My question to the ATSF experts: was there is rule or time period for either of the two positions.
From what I can tell in my own research, ATSF started moving front locomotive headlights from the numberboard area down into the nose in the late 80s/early 90s. Often the rotary beacon was removed and the air horn was moved from the cab back to the long hood. Some also got ditch lights, but this may have come later. The best advice, I think, is to look for reference photos of the particular locomotive you’re modeling.
Also, the same locomotive may appear different at different times. I am working on an ATSF SD40, for example, and debating whether I want to model it with the cab headlight or nose headlight. Both are correct, depending on the year.
Other details change, too, like awnings behind the cab which some ATSF diesels had in the 80s but most of these were later removed.
Motive power annuals from the time period you’re modeling are invaluable. You might be able to find some on eBay or at train shows.
There are also some good sites on the internet with pics of locomotives. My hat is off to the folks who maintain these, as they’re an invaluable resource to us modelers. A few I frequent are:
http://www.rrpicturearchives.net/
http://www.rr-fallenflags.org/
There are also some ATSF specific sites I’ve found:
http://rlehmer.50megs.com/photos/ATSF/