[Richard]

This is still a brain tease.

Over the years I have learned to assume nothing.

Would you humor me, and post pictures of your 12v pump and of your 120v pump?

I am asking because of the picture you posted above of your pressure control switch. Both the 12V pump and the 120V pump have their own pressure switches. If you pulled the cover off the 12V pressure switch, your readings would make perfect sense. Is the picture you posted an actual picture of YOUR switch, or of an internet photo? Because another clue would be the gauge of the wires connected to the switch.

This obviously is a pic of a well pump switch.    

And this is a pic of a crusty relay box that is associated with the HWH leveling system. Newell used it to take the 12V signal from the HWH and bypass the 120V well pump switch. Do you have one of these boxes?    

I am thinking one of two things. The 120V pump wiring was fouled up during the generator work(likely)or you may be possibly confused on which pump is which ( not likely).

[bestgenman]

Looking at the picture of the pressure switch with blue circled contacts, I have this thought to add.  This is a two pole switch and the measuring points indicated are of one set (pole) of contacts.  When closed, there would be no voltage across them. When open, and the voltage is 12V, it indicates this was surely connected to a 12VDC circuit.  Maybe I’m overlooking something here or seeing zebras!

Was the meter reading volts AC or DC and could it be millivolts?  Digital meters have pretty small letters to indicate the range and my tired old eyes have difficulty identifying.

The fact that this all changed when the generator was removed and reinstalled is certainly a clue to this dilemma.  I’m with Richard, still baffled from the data!

[Parisjet]

I learned a lot about this system yesterday while fault tracing my compressor not coming on. I had checked everything i could think of. I had line voltage at the control box in the compressor bay as well as low voltage (34vdc) but no power to the compressors. My coach is plugged into shore power 50Amp and all of the other electrics were working normal. My switch in the galley will turn off the power to the compressor control box (where the #1 & #2 priority switch is located)
I then noticed that the screen on the Siemens small green box was blank. Just on a lark, since i had spent hours checking everything else, I thought I will try starting the coach and just see what happens. When I turned the ignition key I got nothing, chassis batteries were totally discharged. I then flipped the emergency switch on and the lights came on the dash and to my surprise the compressors started running. I looked in the compressor bay and the screen on the Siemens box was lit. so here is the takeaway on how the system is wired.

• The Siemens box controls the compressor circuit and according to the factory it controls the pressure  low-on / high-off . The Siemens box gets its power from the chassis battery and not the coach battery or the inverter or the shore power.
  
• You must have a good chassis battery for the compressor (control circuit) to operate.
  
• The power for the compressor can come from the shore power or the coach batteries via the inverter.
  
• My compressor 120v switch in the galley turns the compressor on/off, it will not run with the switch turned off.
  
• I am adding a battery minder charger today to make sure that the chassis battery is fully charged. I can keep it charged with the emergency switch but have heard that this isn't a great idea long term on battery life.
  usually there is a fault trace diagram that would have made this easy to diagnose, I may have to draw one up and post here. It would have saved me at least 3 hours of fault tracing without a diagram. The top line would go like this. Check to see if the Siemens control box is lit, if not check the chassis battery for 12v or more.