The number light switches on the rear panel are marked front and back. However the "Front" switch turns on the right hand side lights front and back, whilst the "back" switch turns on the left hand side lights front and back.
Maybe the front of the loco is relative... who knows what's in front of the universe... perhaps it's the right side of the SD40
It is a little known fact that EMD originally designed the SD40 to go down the tracks sideways. But railroads refused to operate it this way, so eventually EMD gave in and changed the number plate switches.
