Location is more then just a preference. Visibility is the biggest reason they are placed at the belt line. 39 taillights were an after thought signal light option and GM re-used an existing part. Even in 1939 these taillights rode high on the belt line. I have seen, what I believe were dealer installed 1939 lights lower than the belt line, so it may have been left up to the discretion of the dealer who installed them or it could have been a body shop or owner that placed them low. Today, they are placed wherever the owner wants them and that's ok, the truck itself is the attention getter, not the signal lights. Me, I prefer them at the belt line I want the people behind me looking at that level not at my rear bumper.
