Battery Isolator Switch

Hi Everyone,

I have an issue with battery drainage in my defender and i am assuming that installing a battery isolation switch would help me solve this. I would just need it as a security measure that the battery will not drain if parked for a while. Can anyone help me with recommendations for a switch and installation?

There are lots of cheap but reliable ones on Amazon or eBay - personally, I'd recommend one with a removable key, given that the battery is under the seat, so one that isolates on the terminal is a pain.

I have fitted mine to the seat box before, just need to be sure your passengers won't damage it getting in and out of the defender.

I prefer isolating on the negative, but either works - go from battery to isolator, isolator to original cable that would have attached to the battery - job done.

If you've got alarm systems etc fitted, you'll need to wire these to always connect to the battery, but they could be the cause of your drain, so I'd suggest figuring out the cause of the drain is as important as isolation.

Thank you.

I have seen a lot of people talking about if it was accidentally switched whilst using the vehicle it can damage the alternator. Do you know an easy solution to prevent this?

I did both mine, as said above switched the earth, used a heavy duty metal switch, as was suspect of them plastic red ones, even though our boat has three of them red plastic ones which are original and boat is 1994!
If I was to do it again, I would use a remote switched one with a small switch hidden on the dash in plain sight.

Salmxn said:

Thank you.

I have seen a lot of people talking about if it was accidentally switched whilst using the vehicle it can damage the alternator. Do you know an easy solution to prevent this?

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It's really down to where you position it really - I fitted one near the footwell and regretted it because it was always at risk of being knocked.

In my series I mounted onto the bulkhead, that was much better.

Buy a switch and tape it in different places, see what's convenient

I have one of the terminal ones on the negative in the seat box. I cut a hole in the lid so only have to lift seat to activate.

I had one of the red key types in my previous D90. It was on the front of the seat box and my passengers would often knock it off.
After a while I never bothered to turn it off and hide the key and then it got stepped on and the key snapped and it was always on...

I have contemplated using a wireless/key fob remote switch/relay but I think, in your case, i'd concentrate of finding the drain.
Fitting an isolator isn't curing the promblem it's just masking it ...

lynall said:

If I was to do it again, I would use a remote switched one with a small switch hidden on the dash in plain sight.

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That is what I have just fitted to mine as part of the rebuild I used one of these solenoids: LINK (Operating: 400A, Peak 800A (22secs))
I just use a toggle switch to operate it and have a safety cover on the switch so it cannot be accidentally activated. I also have a 2.5A fused ling between the terminals of the solenoid so I still have power to the vehicle for interior lights, clock, radio settings, and most importantly the switch to activate the solenoid, but any load will blow the fuse and immobilize the vehicle (e.g. as soon as the ignition is turned on there is too much load)
However I do not know if this woud solve you battery drain issue as obviously the battery is not fully disconnected in my setup so a low power drain would still be present.

You are much better fixing the drain than trying to fix the symptom.

dag019 said:

You are much better fixing the drain than trying to fix the symptom.

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Word...

To prevent damage to the alternator, just buy the FIA master switch as that kills the engine, isolates the battery but protects the alternator.

Had one on all of my LR's since 1987 inc. my 300TDi 90 that I sold a couple of weeks ago. Mounted on the front of the passenger seatbox adj to the tunnel, it was never accidently knocked or operated yet is in easy reach of the driver.
With removable key it is also a handy security device but to keep alarm, Skytag etc operating I ran a separate, small, fused, non-interrupted supply.

I've got one of those master switches installed in my Disco 2's engine bay for the winch circuit.

You wouldn't need the additional terminals and resistor for a winch circuit though.
A normal On/Off would do for that.

Yep. I've got it connected to my negative cable of the winch to the battery.

JUKE179r said:

Yep. I've got it connected to my negative cable of the winch to the battery.

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Thats an odd way to do it, you still have a big, fat, 600A carrying, live cable out to the front of the car ?

i use thye durite keyed oe in both my 110's fastened to the seat bulkhead front

A

miktdish said:

Thats an odd way to do it, you still have a big, fat, 600A carrying, live cable out to the front of the car ?

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Never connect a disconnect switch to positive cable mate. Only negative.

JUKE179r said:

A

Never connect a disconnect switch to positive cable mate. Only negative.

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What is the reasoning for that? Both my winch and my main engine are connected to the positive. And ones on the stage rally vehicles I work on also have them connected to the positive.

dag019 said:

What is the reasoning for that? Both my winch and my main engine are connected to the positive. And ones on the stage rally vehicles I work on also have them connected to the positive.

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I’ve done this in the military and carried on connecting the disconnect switch to the negative battery cable.

Here is a website mentioning it but real no true reason for using the negative cable:

JUKE179r said:

I’ve done this in the military and carried on connecting the disconnect switch to the negative battery cable.

Here is a website mentioning it but real no true reason for using the negative cable:

https://www.motortrend.com/how-to/kill-switch-positive-or-negative/amp/

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I am just curios, my tractor and series both have manual disconnects on the negative terminal was more if there was a specific reason.
the winch in particular as above I agree should be positive as the battery is still connected so if there is a failure you have a live heavy gauge cable shorting if the winch isolator is on the earth.