Lots of older trucks were positive ground. Some had 24 volt starters. But that is a different story.
Your TT is Negative ground and I suspect that is why the fuse you found is blown. I hope nothing else is damaged. Your converter may have fuses to protect it so be sure to check the voltage on the battery after you correct the error. Many converters have diodes and fuses designed for that issue.
Take a picture and call the dealer in case there are other items that were damaged.
Myron & Deborah
08 HR Endeavor 40 SKQ
2012 Ford Edge Limited FWD 3.5L
Aluminator tow bar, Demco base plate