Battery Isolator Cut-Out Switch Location anyone ?

[rfs1957]

There are many references to using an (I assume ?) earth-lead circuit breaker switch on the main battery earth, both (I assume ?) for security purposes, to reduce the risk of impromptu fires, and to make it easier to work on the car without dismantling the battery post connection each time you are anywhere near wiring or petrol.

I'm curious where people source their cut-outs since all the retailers appear to sell the same stuff, whether they are simple single-pole breakers that just do fat cable interruption, or ones that have a parallel ignition circuit interruption switch that I think is designed to prevent over-run.

Could we have an exchange about the pros and cons of these ? I had been going to fit the former, with a fused bypass just for the clock. I'm still on +ve earth, and since I still use the original Dynamo don't think the Alternator pull-down facility of some of these switches is relevant to me, at least ?

A good coverage of the function and cabling of the more sophisticated type of these switches can be found here, although in this context it is being used just to stop the starter motor functioning - so is fitted on the live or non-earth side of the battery.

https://www.pegasusautoracing.com/docum ... =TECH00109

The other consideration would be : where do people fit and access them ?

On my RHD 3.8 I had been going to use the type with a big red removable key, fit the switch through a master-cylinder blanking-off plate above the passenger footwell (shell untouched), and thus access the switch with the key through the footwell - reckoning it was easily accessible in case of fire, and when I forget to turn it on etc

Perhaps someone could start the debate ?

[christopher storey]

You want one which is easy to use, or it will be too much trouble to use it . I think a simple racing type red handle is fine, and your suggested location also

[mgcjag]

Hi Rory....yes they are a good idea.....mine is just one of the standard type fitted onto the earth post...so i have to lift the bonnet and unscrew a knurked knob to disconnect......very non elegant.......If your considering a rewire to a key solution it may also be worth thinking of adding a socket/connection of some type so you can plug in a trickle charger

[Simon P]

I've got the same sort as Steve - mine's mainly just to lessen the chance of a flat battery if the car's parked up for any period of time. I flip the interior light on, twiddle the knob 'til the light goes out, and then I know the electrics have been successfully 'cut'. Likewise when returning to the car and re-establishing the circuit, the interior light coming back on (or not!) gives and immediate indication of whether everything's still healthy.

As mine's an S2 the clock has its own battery so I don't need to worry about a fused bypass for the clock.

[Polse7317]

HI , above that is what i have done:


I'll have an acces without opening the bonnet

[rfs1957]

Yves, Avez-vous eu mon message privé ? Slts, Rory

[Polse7317]

Sorry Rfs i have no PM....

[Moeregaard]

I fabricated a small bracket that secured a Hella racing switch to the fluid reservoirs' heat shield (LHD car), switching the earth lead. Obviously, this could be defeated by a determined thief with tools, but for the casual criminal it was adequate. I probably should have located it inside the car, but didn't. I did turn the electrical off when the car was garaged. Even though I replaced the entire wiring harness during restoration, I always felt better going to bed knowing that the car couldn't barbecue itself in the night.

[nottsman]

I have kill switch with the removable red key, not racing spec but isolates the car when in the garage and when parked away from home.

I made a bracket out of aluminum sheet and attached it above the battery, painted black and looks quite neat. Can't post a pic as I'm on hols in Italy at the moment.

I am looking to relocate to inside the car and have removed all trim, centre console etc as part of my restoration. I am considering using the cigarette lighter hole to hold the black switch.

I'm also quite taken with the bare metal look of the gearbox tunnel and not replacing the radio and speaker console. Hope I haven't upset any purists!

Nick

[david muir]

Hi Rory,
Initially fitted a Lucas cut-out to earth post on battery( obsolete but one on Ebay right now -EBay item number:162124398495)
. Subsequently, with a view of isolation from inside car if 'smoke started escaping', fitted a Lucas switch going through blanking plate to passenger footwell (RHD) exactly as you describe. This second switch is not visible when looking into car and sits just aft of passenger footboard (wooden 'option' which shortens the footwell).
Considered run-on etc but reckoned I would always have switched off ignition before battery isolation in 'smoke situation'.

D

[tim wood]

When I converted my alternator to the type with a built in regulator this left the spot where the 4tr was fitted spare.
Thus I used this to locate my cut out switch.

Sourced a unit from Durite which has been good so far.

Will try to post a picture

Tim

[rfs1957]

Here's the usual type of cut-out switch fitted to a footwell blanking plate, hopefully like Angus meant ?



It interrupts the earth-lead, obviously, so far so good ............

BUT how do I run my clock now ?!

The idea of fitting it was less for anti-theft (anyone getting the bonnet open can see what's going on) and more for won't-catch-fire-whilst-I'm-asleep ...........

I wondered if I ran a couple of small wires, off the small Lucar spades I've added, you can see them just abouve the main cable posts, up to a cartridge panel-type fuse - perhaps in the glove-box ? - with say just a 2A blow rating, would that give me :

a) enough current to run the clock, AND the interior lights since they'll have to operate getting in and out ?

b) an easy way to change the fuse when I constantly blow it by forgetting to switch the cut-out back "ON" ?

What does everyone else do, please ?

[mgcjag]

Hi Rory...you do mean you have it in the live and not the earth......for the clock yes just run an aux fuse you wont blow it if you try to start as you can wire it on a seperate Cct.....but the interior lights is one of the main reasons for a flat battery, not switching them off overnight.......you coukd also wire in a socket for a trickle charger

[rfs1957]

No Steve, it interrupts the eath-strap circuit - I'm still a positive-earth-and-dynamo man, at least until it packs up on me I am !

But the fuse would fulfill the same function - the clock's live the whole time, it would just get its earth via the feeble fuse.

So it WOULD blow everytime I forget it .............

After looking at all sorts of unnecessarily-complicated plugs and sockets, I ended up just putting a pair of RadioSpares 4mm banana-sockets in the alloy floor panel under the battery, one Red, one Black, and I just charge the battery directy via a flying lead - but via a 2 amp in-line fuse on the car-wiring side.

[mgcjag]

Hi Rory...whats the reasoning for isolating the earth side and not the live side........if you isolate the live then you can run independant ccts for the clock etc with out blowing the fuse if you try to start without switching on the isolator

[rfs1957]

I think my reasoning for doing it on the earth side was that

1.it didn't make any difference to the function (big "ahem" - apart from the clock !),

2. that it was much neater to cable it that way on my car, with the battery fitted that way around, and

3. if you do fit it on the LIVE side, you still have to be careful about spanners or w.h.y. dropping on the LIVE battery terminal because they can still short to ground and put weld-marks on the LH wheel-shield, and

4. you would end up - on the type of cut-out switches we all seem to use - with another two exposed live terminals that you can drop tools on !

But I may yet have got it all to cock and am happy to be corrected.

[EbenTian]

Hi..i am a new user here. In my case it is just one of the standard type fitted onto the earth post, so i have to lift the bonnet and unscrew a knurked knob to disconnect.If your considering a rewire to a key solution it may also be worth thinking of adding a socket.

[johnetype]

For those using a fuse to bypass the isolator to keep the clock running, I suggest using this kind of automatically resetting fuse - see eBay 221730487323 for an example. That way, if you forget and try and start the car you won't have to keep replacing a blown fuse.

[rfs1957]

Thanks for everyone's inputs here.

I'm still open to suggestions and corrections about putting the cut-out in the Earth side ?

My points 1 to 4 as to why I did it that way were not at all intended to put an end to the debate, especially as I made them up retrospectively anyway !

Have I done "the right thing for the wrong reasons" after all ?

[Whitact]

One thing to look out for when fitting an isolator is additional voltage drop. When fitting the relay upgrade to my headlights I found that the isolator (red plastic key type) fitted by a very well known specialist was responsible for more than 0.5v drop. Fitting a new isolator reduced that to a negligible amount.
Cheers,