I give up.
It seems to me that the intention of brake lights is to signal to a following driver that you are slowing down regardless of HOW you are doing it-service brakes, jake brakes or dragging your foot. I don't have jakes(unfortunately) but I think they slow you down.
that's what I do if I see some dumb @$# behind me cumming up fast dave
the millions of trucks on the road you never see a 3rd light warning for engine brake use