Just speculation.....but any engine zincs that are on the salt water side would be on the same ground plane as the other zincs that are exposed to salt water. The saltwater “stream” on an idle engine usually remains uninterrupted (due to vacuum) back through the engine intake side to the surface water at the intake strainer thus completing a path to ground. Also the bonding system (connecting all non engine zincs) is usually connected to the engine block (dc ground) in one form or another. Not sure if the engine running or not would come into play here?
|