Messy! The problem is indeed in the switch on the far left. I took it out and stubbed out the wires so the indicators will work when I hold the wires together (and click my heels!)
It does give me a way to see how full the fresh water tank is, though. I'll scout the various electronics stores for replacement spring-loaded SPST 12V switches that fit in the opening. Is it too much to hope that these are standardized?
The green indicator on the "pump" switch is an LED which turns out to have been held in place by bubblegum. I'll have to figure out how to stick it back in place when I close this up "for good."
The rig is vacuumed. The hot water heater works. The stove works. The water system, as reported this morning, works. The refrigerator makes the right noises. The fan on the vent whose cover I replaced works. The solar panel pumps juice into the batteries. The dinette table is stabilized. Slowly, getting ready to hit the road.
A friend read one of my earlier DIY-type posts and asked in the nicest way, "Why are you telling us this?" Because this is kinda scary. And I'm pleased to be tackling it, solving problems, and owning this thing. Lots of progress in the almost 12 months since I got this thing and didn't know jack about how it worked or even what was in it.