Faulty reverse polarity light or not?

[transmitterdan]

The reverse polarity light works by detecting the voltage between the neutral wire and the ground wire. In a proper installation the voltage will be near zero and thus the light stays dark.

When the hot and neutral are reversed then the neutral is not zero volts any more and the light comes on.

Another way this can happen is when the neutral wire is poorly connected between the panel and the earthing point in shore. In that case the voltage of the neutral wire becomes some random voltage between zero and the hot wire voltage. It all depends on what is switched on at the moment. In this case the light will flicker as the neutral voltage wanders around. Plus most appliances won't work because they can't get enough hot-neutral voltage to function. It sounds like in this case that is happening where the shore plug connects to the dock side receptacle. So it would be a good idea to get an electrician to check that receptacle and get it fixed.