12V outlet Tests at 7.4V

Could be that they have separate fuses and the fuse on the outlest with the low voltage has blown---then, you might just be reading feedback voltage. Had the very same symptoms on our trailer and that is what it turned out to be.

Poor conductivity at the hot or ground side. clean up the terminals, connections and where the ground wire attaches to the frame.

Role Reversal

Get a do-it-yourself plug.

7.4 volts across the two pigtails, right?

One of those pigtails is ground. Extend the wire and connect it to a known good ground. Does the voltage still road 7.4? if yes, the center contact the positive connection id bad. Yank the fuse at the panel, dig out your pocket knife and scrape the center terminal shiny.

I will try these suggestions tomorrow and let everyone know how it went. I really appreciate the help.
RichH

Bad connection, VERY BAD CONNECTION somewhere, or a blown fuse.

On some RV's the fuse panel (mine is such) has LED's to show which fuse is history.. This will cause a volt meter to give a reading (low) even if the fuse is blown... Solution, Apply a load (map light or some such) and the LED should light indicating which fuse needs replacement.