I don't have a volt meter and wouldn't know how to use it..
I would strongly suggest you correct that. A motorhome has a rather complex electrical system and unless you can use a volt meter it is very difficult for anyone to help you because we are just guessing. They cost $10-15 at harbor freight or any hardware store. Really not hard to learn the basics of 12 volt and 120 volt testing so that you can provide answers to diagnostic questions.
Some basics:
Your batteries can get charged in three different ways:
1) From the converter / charger in the house
2) From the truck engine when running
3) From your solar panels
If none of those things are charging I would first make sure that the battery disconnect is 'connected'. Have you tried moving that switch back & forth?
Voltage should be:
12.7 volts when the batteries are fully charged and have rested for at least an hour.
13.7 to 14.7 when charging depending on the type of charger and how it is set.
Anything less than 12 volts indicates a serious issue.
If you had a volt meter you would:
1) Test at the battery terminals to determine if there is any voltage (checking for shorted battery)
2) Test at one of the interior 12 volt outlets (might tell if the disconnect switch is working)
3) Check voltage while the engine is running, this should be 13.7 or higher while charging.
4) Check voltage at the truck battery, it should be 12.7 volts at rest after an hour of no charging, and about 13.7 (roughly) when the truck is running. Tests for alternator working.
But without a volt meter there is no way to make those tests and thus not much help anyone can be except to guess.
A couple of questions:
1) Are your house lights on or off? Dim or bright?
2) Does moving the battery disconnect switch make any difference?
3) Do you have access to shore power so you can plug in and run the on board battery charger? Note that charging from the truck engine is more of a trickle charge not the full amount you would get from the converter (charger) in the house.
4) Do you have an on board generator? That will power the converter and do a much better job of charging the batteries than the truck engine.
Running the truck engine for any length of time should give you 12 volt power to the lights while it is running, IF the interconnect is working. There is a fuse under the hood that might be blown that would prevent the truck engine from charging the house batteries. But that does not explain your other problems.
Have battery numbers but the screen doesn't show any.
Not sure what you mean by this, can you explain.
Is there a fuse as part of the battery disconnect switch?
Not the disconnect (as far as I know) but there definitely are fuse in the 12 volt line near the battery. But you need that volt meter to test.
All the circuit breakers are ON.
The circuit breakers are for the 120 volt systems. All of the 12 volt circuits have fuses. The only circuit breaker that matters here is the one to the converter, and that ONLY if you are plugged into shore power.
Maybe the switch is broken?
Maybe. And with that meter we could test for an eliminate that quickly.
May I suggest if you have a friend or neighbor handy that has a meter you get them involved? Really need to be able to tell what is going on.