Lights in an RV are usually 12 volt. So if they are not working CLUE
A/C usually uses 12 volt for Control.. Furnace is a 12 volt device.
Fridge and water heater use 12 volt for control.
If you have a pair of 30 amp fuses on the fuse panel I'd start by checking them.
How to check fuses the easy way... A TEST LIGHT
You can get a test light at most any auto place Prices and quality vary but most all are good if you follow this procedure Also get a coil of wire and the kind of clip you find on the test light Same store shoudl have 'em
The Test light looks like an old fashion ICE pick. clear or translucent handle and a wire with a clip coming out it.
Clip the clip to a known good ground (Negative wire)
Touch the tip to a known good 12 volt Bright light good. Dark reseat the lamp and try again (Testing the light)
now on the fuses each end has a small window
Bright/Bright = Good
Dark/Dark = No Test
Dark/Bright or Bright/dark = Bad fuse
NO NEED TO REMOVE FROM PANEL.
The coil of wire.
Sometimes you need to go some distance to find a good ground.. Strip bit of both ends of the coil.. then re-roll it up with the bare end poked into the middle.. On the other end put the clip. use it as an "extension Lead" by clipping on a known good ground (battery negative?) and then unroll to test area and clip the clip on the exposed end in the middle.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times