Welcome to iRV2 .
There is another post in the Ford chassis forums where a member asks which one of three transmissions his chassis has .
Best guess is that connector ; being as how it appears from the dirt , never to have been used ; is for equipment ( possibly a transmission option ) your coach doesn't have.
EDIT: I see that GypsyR posted while I was typing ; boy I type slow .
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.