Hello
Just wondering that the small oblong object on the cabside of some FL Class 66's is for? Here's one on a photo on Flickr (not my photo, so I've linked it rather than embedded it), with it to the right of the '8' in the loco number 66418 and under the 'er' in Freightliner:
https://www.flickr.com/photos/113420183@N07/21167949324/
Many thanks,
Simon