Seat heaters were included with the Freightliner air-ride seats in the 2016 chassis. It is possible the OP's rig is a late-2016 incomplete chassis with the motorhome completed in 2017 and titled as such. Since the seats were from Freightliner I believe the wiring and fusing is integral to the chassis.
South Jersey Joe - Do you have a DTNA account? On there you can pull up wiring schematics for your chassis. And LOTS of other information. If you don't have an account you can request one as an owner. It takes a few days (weeks?) for them to get back to you and assign you a username.
Here is the website:
https://dtnacontent-dtna.prd.freight...h-america.html
Click the new user button to register for an account.