battery isolation \ security

The Mrs is one of those horse types, well she is irish which should explain it! She has decided to buy a cheap horse "lorry" which will probably be a 1990ish VW LT35 so she can drive it on her car licence. this is great for me as i have a 1990 vw also and i imagine they are mostly the same electronics wise, which will make it easier for me to upgrade for her Ive always been pretty competent with car electronics as they're pretty easy generally, have made headlight relays and wired up total closures and such in the past. Now to say the 1990 LT35's are basic would be an understatement, so im already planning a few upgrades to make her life easier, rearview cameras are really cheap these days, and i can fit her LED spotlights and other things that make her life easier. One thing i would be interested in fitting would be a battery isolation switch, Horse lorrys spend a lot of time not moving, left on yards for trips every other weekend and the battery often goes flat. ive done a split charge relay before when i was into car audio. so im tempted to set her up a leisure battery for the lights and stereo and such. but in order to allow her to start the thing after a long sit at the yard and also for security, id like her to be able to completely isolate the battery. TL:DR The Isolation switches ive seen online I believe have to be situated between the battery and the rest of the system, and as such have to be situated near the battery am i correct? which would make it difficult to hide in the cab? is it possible to have a remote isolation switch that could be hooked up to a switch nearer the cab? or would people be worried that it could be switched off while driving. I was thinking a Relay that was big enough for cranking voltage, if such a thing exists. and a switch to open and close it in the cab. I suppose in this instance the switch would need to be fused and if the fuse went the power would go out. hmm any suggestions?

Sorry sir you're stuck for safety reasons with a switch on the NEG side of the battery. The cranking voltage is 12, it's the 90-100 amps CURRENT on that diesel starter that you have to worry about.

Since it's to prevent discharge of the main battery whilst sitting unused for long periods, next to the battery should be fine in which case it could arguably be in the +12V side. However, it should be on the GND side as Howie wrote - ESPECIALLY if remote from the battery. (Which battery terminal do you disconnect first & reconnect last? (And why?)) For mere isolation purposes, any suitable mechanical "battery isolation switch" should do - ie, a mere single-pole switch. (These should be rated for ~200A or higher or 400A peak to handle high cranking currents which can be well over 200A tho reduction starters often take less.) I advise against any relay implementation. How do you ensure the relay does not open or fail when driving? [ Granted, I know of local competitive vehicles that have such implementations, but they have been passed by Scrutineers with even less expertise & intelligence than their Regulators! ] I did write about hotside versus GND isolation in threads like newbie problem, engine kill switch (page 1) which included a "corrected" version of published the FIA Approved Isolate & Kill Switch. (Despite their recognition that more than a single pole is required to isolate the battery AND kill the engine, for some stupid reason the battery isolator is shown on the hot side (+12V) which IMO should obviously be understood as being hazardous - especially when these switches are required at rear corners of front-battery vehicles! But it's not the first time I have seen stupid ideas and implementations by Regulators.)