What used to be on my bumper?
if your spare tire is underneath the truck, thats normally where you put the foldable jack crank handle to let the tire down from underneath ( next to the plate ).. the other holes were prob lights that were added on as back up lights or sumthing, the two small holes are the mounting holes and the larger was the wires going thru.. maybe it was back up lights for the trailer it was towing..
Since they look simetrical in size and spacing on each side. You may be able to find those black push in retainers for door panels or for lack of better terminology "hole fillers" in the self help section of the local auto parts store. I've used them to cover holes in motorcycle body panels where POs drilled holes to mount lights. Also if you dont want the black to show you may be able to color match your paint with a Duplacolor touch up/scratch paint pen or small bottle with a brush.




