Electrical Problems Are Not Simple – UPDATED

Updated: I posted a question about this on the excellent Sabre Owners newsgroup and received some great suggestions that I added to the bullet list below. Since we launched Cadence for the season, we have been plagued by an electrical issue. We're sailing along, minding our own business and suddenly, everything shorts-out. The chartplotter and VHF flicker on and off, sometimes die. The voltmeter at the panel shows the batteries down below 8 volts. We switch everything off and the voltmeter reads around 12 volts (not good but enough to start). We crank up the engine and everything returns to normal for a while. Then the problems re-occur even with the engine and alternator running. The joy of being in a yacht club is that there are lots of people willing to help and no end of opinions. One of the recurring opinions is that electrical issues are simple. It's all down to breaks and shorts. Not so much in my view. So far the more helpful opinions have been:

• Load-test your batteries. Done that and they are fine
• It's a grounding issue. I checked the main ground and it's fine
• There is an electrical leak somewhere. Agree but can't find it.
• The newly installed solar panel is the problem. Disconnected and it didn't fix it
• The recent rewiring of the bilge pump directly to the batteries is the issue. Could be.
• Faulty voltage regulator. Sounds plausible
• Gremlins. Most likely
• Engine gauges are grounded to the keel bolts need cleaning (not sure that this is the case with my boat)
• Loose connection at one of your primary connectors-most a main ground at the engine. Don't think it's this as I have checked all this carefully
• Chafed wiring harness. This is sounding likely as multiple systems would be affected by this. The wiring harness that contains most of the grounds which is on top of the engine (almost all yellow wires)
• Other advice: Start by installing a monitoring system
• Get the very best reading you can of the actual battery voltage
• The truest words: "The fix is most likely simple, finding the open connection is the difficult part."

I read the excellent 12-Volt Bible, cover to cover and tried a number of the suggested tests. Frankly, this only left me more bewildered. I even tried a painstaking leak test which suggested that half the circuits have leaks in them. Oh, goodie! I have thrown in the towel and taking the boat back to the marina to have the electrician work on it. Ah, the joys of boat ownership.