2 problems

Polarity issue, maybe?? I have always plugged my rig in at home with a 2-wire utility cord and never had a problem. My new rig has a power management system and nothing would work. The power management system gave a polarity error code. I flipped the plug over and it's all good.

I replaced the two coach batteries and everything is again working 100%. Thanks to those of you that suggested the batteries, I did not realize how important they are to the entire electrical system in the RV.

Some converters have to have a battery to work properly if you have dead batteries it will have an effect on the 12v from the converter.

One more thing to consider is some rigs have power management systems that shut down systems in order of importance based on how much power is being supplied. Now, that doesn't explain the "furnace" (which is probably propane with a DC control board)... unless you mean an electric heat pump. As for the fridge, if it's AC or propane, I can certainly see how the management system would shut down the AC side when, for example, the batteries are low and all of the available power is going to the charger... or a cycling electric water heater, for example. 110volts is not much for a coach... assuming you're even getting that much, concerning the gauge and length of the cord.

I'm thinking I have a problem with the extension cord I am using, we are staying at my son in laws and just using a small extension cord, as this was a quick setup and I forgot my good cords at home. The steps are acting crazy, lights are flickering, lots of issues, I'm going to stop by home and get my heavier cord for starters to see if that works, then I'll go and get batteries for the genset.

I think you need to get your batteries working first, then see if you still have the problem. My guess is that will fix the problems.

How do you know Fridge is shutting off when furnace does?

Other than panels lights on fridge I can't tell when my is running.

Furnace DC is from it's own Fuse and controlled thru T-stat

Fridge needs DC to function whether it is on AC or Propane.

Please explain with more details?

If you are plugged into shore power, and your power is cycling on and off, you may have a bad connection in the 12 volt power system somewhere. Start at the batteries and check for 13 volts or more, when plugged in, and go from there.

Charge or replace your batteries. Then, see if you still have the problem.

Low batteries can cause strange problems. If that is not the problem, you will still need the batteries charged to diagnose the problem.