Thanks for the suggestions so far.
The alternator output is connected directly to the house battery bank, which also powers the N2K bus containing the compass. As a test, I can try to rewire the bus to a standalone battery, but that won't be a solution.
Turning off the alternator is the same as disconnecting it from the boat wiring
. It can't be operated disconnected without damaging it. The external field wire controls the amount of current the alternator produces - if disconnected, the output stops.
I don't understand the ground wire twisted response. Are you saying to make them twisted or not to? Since they run 15' back to the house bank, I'm sure they probably have a twist or two somewhere in there.
This is the only electronic compass on the boat. I didn't notice the mechanical compass at the helm
swinging, but will check on that.
The batteries are located in the saloon
about halfway between the two engines, but a bit closer to the engine causing the issue.
There is no ferrous metal between the compass and alternator other than some odd bits and bobs scattered about like pots and pans, an AC compressor
The compass is N2K. I can try isolating that bus to just contain the compass and short past the length of backbone that runs near the engine.
There are cables
carrying higher current near the compass - the other engine alternator output wires run to the house bank and there is a set of wires running from the house bank to the starting battery via a VSR combiner. This would be very difficult to change. However, the current going to the house bank is provided by the alternator next to the compass that has no effect on the compass. The current returning to the start battery is always negligible (<2A), and provided by the house bank. No other charging
sources like the solar
or mains charger
causes an issue.
Moving the compass permanently would be a large challenge, if even possible. I can move it temporarily and plug
it into another part of the N2K bus to test.
So I have some experiments to try.