In a pile of Mustang parts a friend "inherited" (house foreclosure) there was a trunk light assembly that had a grommet with the coiled up wiring running thru it. It may have been from a Mercury, the p/n on the bracket was barely legible, so the trunk light option may have been a common item to both Mustang and Mercury, and with a grommet required for one, the other got a grommet too.
Jim