Oh , O.K. ;
There aren't any holes per se , those are standard truck reflectors added by the PO and are really common back in the day of only one 6 volt taillight .
If you poke around the site I posted some pix of my truck , I made up some passing warning signs out of the reflective tape they use on school busses and stuck it to the rear bed header underneath the tailgate , inconspicuous untill hit by any light at all in the dark then they light up brightly....
If you like those reflectors , remove them and take to a truck shop & ask for a new pair , under $10.00 the pair I should think .
-Nate