[Carl n Susan]

OK, I am confused by the problem description.

Originally Posted by Dhall0070

So. Sitting inside and the lights went out. Not sure why the TV went out TV. And lights on oven. And air conditioner/ heat pump.dometic thermostat. Fridge All this went out.

All 110was fine

The TV, AC and ridge all run on 120V. So all "110 was fine" doesn't compute. The TV and fridge may be driven by the inverter (which takes 12V from the batteries and makes 120V) but the AC definitely uses only 120V (unless you have added a huge battery bank and solar).

So went to checking. Battery's. 12.9 volts. So plugged in truck didn't help.
Starting checking 12 vt with meter.
No voltage inside the panel at all.
Checked red key disengage no power.
Checked breaker and small pergo swith at battery. I have 12 volts.
Turned on converter and fridge works. 12 volts at converter.

What panel has no voltage at all?
The Red Key - is it in the position where you can NOT removes the key? Is there 12V on either sides of the switch?
What is this " breaker and small pergo swith at battery"???
Turned on converter? Are you referring to the "inverter"? The converter is part of the power panel and it is unusual to have it OFF.

So. 1 4 gauge red wire going to red key switch has no power?? Trace it to the picture. Looks like a regulator of somekind.

Was the Red Key in the position where it could be removed? That switch feeds 12V to converter/fuse panel from the batteries for most 12V devices. If it is not passing 12V, then 12V does not make it to the 12V power distribution panel nor does 12V make it to the battery to charge it. The hydraulic system is powered directly from the batteries and doesn't use the path through the Red Key switch.

Unplugged the yellow and white and power Comes back on??
So this is where I'm confused. The regulator looks like it controls the auto level.?? Why would this cause a problem if I'm not using it.? If I leave this unplugged what will this cause??
2019 3811 montana

What you call a "regulator" is the reversing solenoid for the hydraulic system. That yellow/white wire appears to be one of the two feeds from the switch you press to extend or retract the slides. You will not be able to extend or retract (depending on which one it is) the slides with it disconnected.

Better pictures of the battery compartment would be a big help. Take the pictures in Landscape mode to avoid the rotation issue.

I agree with BB_TX that the self resetting CBs may have failed. But that doesn't explain no 12V on both side of the Red Key Switch. not the loss of 120V to the AC nor why the inverter quit supplying 120V to the TV and fridge.

Here is a link to a 12vdc troubleshooting flow chart:
https://www.montanaowners.com/forums...ad.php?t=86323