Earlier in the week, I blogged about my electrical issues. I eventually gave up trying to fix it myself (not a long trip) and took the boat to the marina where the Great Joel, the excellent contractor who can fix anything, resides.
It took Joel a good few hours of poking around to get to the bottom of it. It turns out it was a ground issue, specifically the ground cable back to the panel was the root cause. As a result there was a 3 volt drop between the batteries and the panel.
Apparently, the cable was old and knackered (like its owner) and now that it's replaced, I am hopeful that the issue is fixed.
Over the last few weeks there were many opinions offered, fairly evenly split between a short or a ground issue. The "grounds" had it.