Here is the procedure for determining whether DC (galvanic or stray) is flowing through the safety green wire onto or off of the boat:
1. Unplug the shore power cord at the pedestal.
2. Put the black probe from your DMM into the ground slot in the pedestal.
3. Put the red probe from your DMM on the ground prong on the disconnected shore power cord.
4. With the DMM on Volts-DC read the voltage and note if there is a negative sign before the reading. If there is a negative sign showing, reverse the leads. If there is no negative sign, proceed.
5. Now here is the tricky part: Electrons do not flow from positive to negative
(red to black) as we are accustomed to and we are interested in electron flow here.
** If the red probe is on the boat side and the black probe is on the shore side and you are getting a positive reading, then current
is flowing onto your boat from the shore side.
** If the red probe is on the shore side and the black probe is on the boat side and you are getting a positive reading, then the current is leaving your boat.
Hope this helps.