negative battery master switch

[Havant-a-clew]

Ho, ho, been havin' fun fitting an inverter (1000w continous, 2000w peak, modified sine wave type, £99 from Towsure). As would seem obvious, connect positive to common oot on battery master switch and negative to earth, Hmmm, didnae seem tae work. Much fekkin aboot wi'a multimeter eventually reveals that that either previous or original owner had fitted the battery master switch tae the negative side o' the system! Why in the guid Lords name would somebody do that. 'Twas re-engined aboot 7 years ago (wi' a Beta) and wonderin' therefore if the original had a positive earth. D'ye think there could be another reason? Wi' the connections sorted, it's a bonnie piece o' kit and runs a wee 1kW kettle or a 1200w microwave, we daft softie Southerners need oor home comforts.......well, if yer plannin' on luring the other half onboard fae a weekend, you do. But ah'm left wonderin' why somone'd wire up ass-backwards. Lookin' forward tae hearin' any ideas.

[sahona]

Negative isolation makes sense. one switch in the line that is common to all batteries ensures the thing does what it says on the packet -"isolate".
I bet you've got one or two wires directly connected to the positive terminals of one or more of your batteries. They won't be isolated by the usual 1-both-2-off switch.
next - are they fused, or could they be the cause of the future fire?
I know we need radio memory (yellow wire) and like to have the navtex and weatherman ready to read on arrival, maybe a bilge pump as well, but really we should isolate totally when away for any length of time.