I have the 2019 (2018 chassis). Disregard the (Sprinter Chassis) fuse block. Unless they updated the system in the 2 years, all else should be the same.
If you have 12 (ISH) power on one leg, you may have a loose and/or bad wire or connections somewhere.
2019 Thor Chateau 28Z 2018 E-450 Chassis W/ V10
4 Wheel tow a 2021 Ford Ranger Lariat 4X4 W/ Blue Ox Alpha Tow Bar/Base Plate and Stay-IN-Play DUO Brake system.