I just rewired my truck ... it had no backup lights, but there were two ambers below the tailgate that were being used as turn signals. So, when I rewired, I changed it so that my brake lights also operated as turns, and I wired the ambers for backups.
Next I'm gonna buy two backup (white) lights for a 53 Chevy (mine's a 54) and put them where the ambers are.
You can see pics at my site link (below my sig) - see link for "Bed Roll Tail Lights" ... also, I didn't hook up the backup lights to work with my tranny -- instead, I'm using a toggle switch under the dash. It's simpler, and also, a nice way to blink "thank-you" messages on the road.
Alan
54 Chevy Pickup