A galvanic isolator is a passive device which protects the vessel from stray currents while it is plugged in to shore power. It has no function unless you are connected to 110v/240v shore power. It is usually found behind the AC panel for shore power, somewhere between the shore power connector on the outside of the hull and the boat AC panel.
Try these links for an explanation.
http://www.marinco.com/productline/galvanic-isolatorshttp://www.marinco.com/files/support/pr ... 531011.pdfThe wiring diagram shows the AC line and AC neutral from shore power running directly to the boat AC panel, bypassing the galvanic isolator. The galvanic isolator, in normal operation, interrupts the shore ground and the boat ground. If fault occurs, the boat is grounded to the shore connection and safety switches are activated. A 12 volt line between the galvanic isolator and the boat AC panel operate the warning lights indicating reverse polarity, etc.
I made a simplified sketch at
http://www.amnet.net.au/~jfair/galvanic1.jpg and found a proper wiring diagram at
http://www.amnet.net.au/~jfair/galvanic2.jpgCheck that the warning lights are not burnt out.
John