(2017 Promaster City) Overhead courtesy light switches have about six positions- but none turn on the cargo area lights. Is this the design, or is there a wiring problem?

Don't know. Sorry.

Clay Lancaster, I think most cars have the same setup, but in mine I don't have courtesy light switches, my dashboard Light is switch or roller or whatever setup you have for your dashboard and that controls my overhead light. Hope you understood me. Oh, and your outside lights have another switch bond that you never touch if it's a newer car they are usually set to come on by themselves.