Originally Posted by Tony B
........... Moral of the story - always have a multi-meter when in doubt.
A multi meter is a bit like a violin. It's of little use unless you know how to use it.
To be specific, one not only has to know how to set the controls, one has to know where to place the probes and what the resulting readings mean.
I'm a bit surprised nobody markets a plug in tester for marina outlets similar to the ones available for 120 volt AC outlets found in homes and businesses. They cost about $10 and test for correct or incorrect wiring and many test the ground fault feature or GFCI outlets.