Originally Posted by Rivatar
if the plug at the marina end is not completely pushed in, the list sea air causes a short between the exposed prongs on the plug, and lights up the reverse polarity led on your control panel
A poor connection between the shore power
cord and power post can cause the reverse polarity indicator to light, but this is not due to a "short" (circuit) or sea air (directly), it is due to an "open" circuit.
The neutral and ground connections on the vessel shore power
cord, (when disconnected) should be open circuit. When the cord is plugged into the marina power post, these are connected (by the ground/neutral connection at the marina service).
If the ground connection at the power post (or vessel shore power inlet) is poor (open circuit), it may cause the reverse polarity indicator to light (even though line and neutral polarity is correct).
But in the case of the OP, there is no problem; he assumed the "test" switch was to test for a reverse polarity condition in his connection. It is not. It is to "test" the reverse polarity indicator.
If the reverse polarity indicator is working properly (as may be tested by operating the "test" switch if applicable) it will light the instant a reverse polarity (or may if "open" ground) connection is made at the power post, with the vessel main AC breaker in the "off" position (where it should be when the power post connection is made or broken) until the reverse polarity check is completed.
ABYC standards have called for reverse polarity indicators for many, many years. If your vessel is post ~1980 or has had AC panel modifications since, it should have one. If your vessel is older and doesn't have one, it is likely way past due an AC electrical