Although Funfinders and Springdales are both owned by Thor, Funfinders are made by CruiserRV and Springdales by Keystone. You might search for a Keystone owners forum for more detailed answers.
Having said that, all trailers are somewhat similar in how they operate. Your interior lights should run off of 12V so that is where to start troubleshooting. Is your battery fully charged & connected? Most Funfinders have an inline fuse on the main battery power line, not sure about Springdale but would be a possiblity to check. Most Funfinders also have a a battery cutoff switch located in different places on different models. Again, I have no idea if Sprindales have this feature, but it's worth checking to make sure it's turned on if you have one.
You said there's a red light on the converter fuse panel. What brand of converter do you have? Does it also have circuit breakers as well as fuses?
Do any of your other 12V items work? Good luck with your troubleshooting. Hope it turns out to be something simple.
2011 Chevy Silverado Crew Cab 4X4
2009 210 WBS