My 2018 Vista Cruiser...... Dometic fridge light quit working.
Bulb checks good and switch checks good.
The trailer is 2 weeks old!!!!
Dealer is 300 miles away!
Try taking off the exterior cover and check to see if any wiring connectors have come loose. Next see if any other items in the unit are not working in which case you may have a blown fuse, also not good for a brand new unit. Does the warranty paperwork specifically state that those guys are the 'only' dealer that will work on the unit?