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Battery cut off switch (groan)


myothercarsa2cv

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Matt the resistor in the FIA version is to to earth any current being generated by the alternator if the switch is used to kill the engine whilst running - something that may happen after a "racing incident".

 

If the use is only for isolating the battery to prevent current drain (eg from immobilisers etc) then it's not necessary.

 

I've heard of several FIA switches causing electrical gremlins, but never (until your post) of a non-FIA one, and assumed (without any evidence!) it was something to do with the extra connections for the resistor on the FIA version.

 

Contrary to Rogers supposition, I'd guess that the switch on a well used road car probably gets a lot more use than that on a race car, as most people seem to use the switch out of habit at every stop.

 

I've had a bog standard non-FIA switch fitted through the bulkhead above the passengers knees, and connected in the negative feed from the battery, for many years (probably 25,000 road miles), and never had a problem with it (that'll curse it now!).

 

Being under the dash out of sight it's very unlikely that some scrote will nick the key if it's inadvertently left in, and if the key is mounted thoughtfully, it's impossible for it to be knocked to the off position by a restless passenger *wink*

 

Very simple to fit as it's the same side as the battery, so less volt drop, and in my case I think only one extra cable was needed from the switch to the battery negative terminal.

The only item I have that is connected directly to the battery negative is a dash mounted ciggy socket, into which I can plug a charger/conditioner easily.

 

An easy and straightforward mod that I'd commend to anyone.

 

A few pics of my installation here (I don't seem to have any of it after wiring, so must take a few more 😳):

 

Battery Switch terminals

 

Pax footwell

 

 

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Ian - haha - that's exactly where the bulk head cut out switch is fitted on my brother's car. Indeed it does make for handy access, and it even looks like you have used the same switch. Even your accessory power socket/s are the same type and positioning :)
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That's where i have mine as well, in the posative lead. I have removed the extra power feeds from the battery and relocated them to the stud on the isolated side of the switch, so it is fully isolating.

My switch is mainly for isolation, rather than security so i tend not to remove the key unless i am out and about. I don't carry a spare, but have tools, so could bypass the switch if i do loose the key. I have not fitted the fia resistor as the switch is not for safety. If i ever did need to kill the engine i could always switch the lights on, these will do the job of the resistor anyway.

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Thanks all, will give the negative switch a go. Any recommendations for getting a lead made up in the NW Kent area? Will probably have to get a longer one, and reuse the existing one between switch and battery?

 

I have an idea that will ensure I remember to take the switch with me when I get out the car 😬 Ta da! One of these between red key and ignition key, and I'll never have a flat battery again 😬

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