On Wed, 23 May 2007 12:46:41 -0400, Wayne.B
wrote:

Whatever the cause of neutral and ground being tied together
somewhere, I suspect it has been that way for quite awhile.

The discovery process continues, thanks to everyone who has chipped in
with advice.

Here's the latest:

The AC neutral and safety ground (normally white and green) are
definitely tied together. As I understand it, this is an ABYC
standard although somewhat controversial. The AC safety ground and
the boat DC grounds appear to be totally isolated however.

I was able to buy a non-contact AC current probe at Northern Tool this
afternoon for $16. It is very useful for tracing out circuits and I'm
beginning to make some sense out of the wiring scheme by turning on
one breaker at a time.

The two bus bars that I located earlier are both for safety grounds
not neutral wires. Tomorrow I'll remove some more panels and try to
find the neutral bus. It's got to be hidden away somewhere. Checking
all of the major circuits with a current probe, there appears to be no
detectable return flow to the safety ground bus bars.