There will be one GFI breaker or GFI outlet that all other GFI protected outlets draw from. Standard equipment would be a converter which takes 120v power and converts to 12v to power lights, fans and charge the battery(s). Has an inverter been added to the electrical system? An inverter takes 12v from the battery(s) and converts to 120v to power TV and microwave. How’s the battery? There’s a fuse at the battery That needs to be checked.
Started before and posted after your discovery.
2019 Pinnacle 36 FBTS
2016 Silverado 3500 CC SRW DuraMax/Allison