Racer-X, with the extension cord disconnected from the RV's power cord, disassemble the male end of the cord. The cord should be a 10-3 or three wires of #10 gauge. The wires should be covered with black, white and green insulation. The black wire should go to a screw in the male plug that is brass in color, the white to a screw that is silver in color and the green should go to a green colored screw.
If everything is good so far, open the box that is permanently mounted to the cabinet wall and which the power cord is attached. The wires in there should be hooked up color to color. If they are, hire a mobile repair guy because you're headed into the ATS or Automatic Transfer Switch and you don't want to go there.
All this can be searched for and followed on your search engine and on YouTube if you would feel better seeing a close up picture of the terminals and wires. It's not, I repeat, not, at all dangerous if the 120 vac is disconnected.
Let us know what you find, Okay?
PS: When you have the plug and the junction box open, check that all connections are tight.