That's because most coaches use head & tail light assemblies of automotive manufacturers. The headlight assembly in our coach is that of a 2000 Lincoln Navigator.
You may want to check with a Ford parts dept. give them the numbers off your tail light assembly and perhaps they can help you.
Good luck and safe travels...
Jim & SherrySeward
2000 Residency 3790 v10 w/tags 5 Star tune & Banks system Suzuki XL7 toad