Ron,
Sorry about the misinformation. With the STARTER switch ON, obviously the engine starts. With the STARTER switch OFF and the HOUSE switch ON, the engine will not start. With BOTH switches ON, the batteries are likely combined. Will have to check it with my meter. Yes, I did purchase my boat used; however, in the middle of the 343 production run, I know that Beneteau did change the wiring configuration. Also, on the 343 models with a windlass, there is relay/parallel component that is part of the system.
A lot of folks modify the Beneteau factory wiring to isolate house & start banks. The way it is often wired from the factory you have one battery bus and can add to, or isolate batteries from it. The labeling and description are often "HOUSE" and "START" but this is simply untrue with a single bus battery system. Flipping both switches ON is really no different than using the BOTH position, all the time, with a 1/2/BOTH switch. It is often best to use them like a 1/2/B used as a "use switch" using the house bank for everything (starting and DC loads) and leaving the start switch OFF with an ECHO or ACR type device to keep the reserve bank fully charged.
I have had far too many Benetea and Jenneau owners kill both banks thinking they were indeed "HOUSE" & "START"due to the owners manual description and the two independent switches.
The most common fix/upgrade is to add a heavy duty negative busbar and to re-purpose the "negative" switch (which FWIW is not ABYC compliant) as an emergency parallel/cross connect switch. You can now have an isolated house and dedicated start bank as well as powering the entire system from either bank with either bank isolated. A simple CMD (charge management device) will keep both banks charged.
This switching also allows you to mix battery chemistry or brand. For example I have a customer with a First series, that he races, using Lifeline AGM for house @14.4V then a very tiny but very high cranking Odyssey PC925 as a start battery. The Lifeline bank charges at 14.4V and the Odyssey is charging at 14.7V via a small buck/boost Sterling DC to DC battery charger. I also have a customer with a Sydney 38 race boat that had a similar switch config and they lost all DC power mid way to Bermuda. They
thought the switches were "
isolated" but really it was just one large bank when both switches were in the ON position.
In the next week or two I am re-wring a Hanse that had an incident with a factory switch config. In this case the banks were isolated (not bussed) with just two ON/OFF switches. The start battery failed due to a bilge pump that had been incorrectly wired to the start bank, not house, and a stuck Rule bilge switch. The owner had no way to use his house bank to start the motor and with massive 8D batteries there was no moving them to the start battery box for a jump. He has decided on a Blue Sea 8280 three On/Off switch panel.
The Bene & Jenneau battery switches are
usually made by a French company called Viatemis (though some I have come across have been
no-name). They can be purchased in a red handle or just make a new label for the re-purposed negative "emergency" switch.
Also keep in mind, if you have a thruster, large inverter/charger or large bank and large alternator that these switches are only rated for 150A continuous. They can have pretty bad voltage drop across them at high current and I have had two that have been dropping close to 1 volt with less than 40A passing across them. Both boats had thrusters and large inverters. Even the smallest Blue Sea m-Series On/Off switch can handle 300A continuously, 500A for 5 minutes and 900A for 30 seconds.
