Battery Isolator switch

Post by **M_Temple** » Wed Jan 23, 2008 9:38 pm

I'd like to fit a battery isolator switch on my refurbished 1969 Trav (the big red one like they have in those racing and rally cars!!) - mainly as an anti-theft device but also if I'm honest as a 'flash git bit' as my father used to say! It would seem smart to:
a) have it out of sight , but reasonably accessible.....!!!
b) locate it on the positive (neg earth) 'live' feed to the solenoid from the battery.
c) mount it such that the switch pierces the bulkhead so the connections stay in the engine bay and the wires do not have to traverse the bulkhead with the consequent risk of the wear/earthing/fire sequence of events
d) a location where lengths of high amp cable are minimised from battery to solenoid.

Any advice/difference of opinion on the above, and where would folk recommend it goes/have put theirs?

Also it would seem sensible at the same time to insert a 'main fuse' in the system so if there is any major earth fault (I will be fitting an ammeter for instance) it protects the system. Again any views/experience on location, size and sourcing?

THanks

Post by **alanworland** » Wed Jan 23, 2008 10:08 pm

I have fitted one to my manual pull starter switch MM. It is mounted under the bonnet and I have it mounted directly on the solonoid supply cable bolt via a heavy piece of brass bar (about 3/4 by 1/8 material) the original cable that used to go to the solonoid now goes to the isolator switch, so the switch isolates all power to the vehicle, except for the alarm, which is powered directly from the battery so it can be isolated but still alarmed.
I find it very usefull when working on the car as power can be isolated at a turn, downside is you obviously have to open the bonnet to access it!

Post by **bigginger** » Wed Jan 23, 2008 10:39 pm

But it presumably makes it very much simpler for a thief to disconnect the alarm entirely - doesn't it? V possibly nonsense - I know nothing of alarms
a

Post by **alanworland** » Wed Jan 23, 2008 11:18 pm

Ah! but there's boot/bonnet switches, ultrasonics and vibration sensor and fuel pump and ignition immobiliser, and if the alarm is disconnected - it goes off anyway and still immobilises.
But I do think the big red key is a good idea!

Post by **bigginger** » Wed Jan 23, 2008 11:25 pm

...and there's the answer - cheers

a

Post by **bmcecosse** » Wed Jan 23, 2008 11:37 pm

Normally these isolators are fitted in the battery earth cable run. Main fuse is not a good idea - just fuse the circuits individually. But be wary of fusing the head lights through one fuse - to avoid sudden darkness use a fuse for each filament. To a degree same goes for the sidelights. Fuse left and right individually - and/or fit a warning tell-tale light across each fuse which will light up if the fuse fails. Really then - it's all getting a bit beyond what's necessary for a wee simple Morris Minor!

Post by **MoggyTech** » Thu Jan 24, 2008 4:00 am

Also it would seem sensible at the same time to insert a 'main fuse' in the system

No, this is a very bad idea. You never want all of the electrics to fail in one go. Imagine losing lights, fuel pump and ignition on a winding back road in the dark. Good idea for a Simitar but not for a Moggy.

Post by **M_Temple** » Thu Jan 24, 2008 8:49 am

OK, very helpful, so a clear 'bad idea' response to the main fuse.

I have read in one of the threads some time ago as I recall that a fuse (30A?) in the supply to the ammeter is a good idea in case of wear/earth/fire sequence. What do you think to that?

I have also read in earlier threads that a hidden switch in the fuel pump supply is a good idea - will do this as well as seems smart and easy and my house is down a 100m drive so he should just get to the end of the lane and conk out outside my neighbour.

The big red switch was also to facilitate battery isolation when working on the car as one of you noted - dropped a spanner once long ago on a Hillman Hunter that shorted out to earth from the battery- welded the spanner to the terminal! (Early MIG welding without the IG)

Any experience on where to fit the switch so hidden but easy to get at?(want to avoid lifting the bonnet every time if possible)

Post by **Orkney** » Thu Jan 24, 2008 9:01 am

Fitting one on mine some day, reckon the ideal place is under the dash pod bedhind the steering wheel.
Easy access for the earth wire, would need some kind of mounting plate accross the hole thats there (very visible when you dont have the card pod insert in)
If your keeping the card pod the chunky wiring may interfere with it though, no matter on mine as putting a guages panel in there.

Think i have a spare brand new one here still in the wrapper if your interested .

The fuel pump cut off is a common easy, cheap and effective anti theft measure, used a lot.

Post by **paulhumphries** » Thu Jan 24, 2008 9:22 am

I use this type -
http://cgi.ebay.co.uk/BATTERY-CUT-OFF-S ... dZViewItem
Takes seconds to fit and no alterations to wiring / holes drilled etc.
I'm not a great fan of the cheap plastic types.
I've an electric bike which uses one as the main battery isolator and don't think the plastic key or the actual switch body are designed for regular use and MIGHT wear quite fast - as I can see on the bike.
I've got a decent one for my Land Rover that us all metal with fixed switch but they cost £20+ which give you an indication what a sub £5 plactic one is like by comparison.

Paul Humphries.

Post by **Welung666** » Thu Jan 24, 2008 9:39 am

M_Temple wrote:Any experience on where to fit the switch so hidden but easy to get at?(want to avoid lifting the bonnet every time if possible)

I have mine fitted through the bulkhead so the red key goes on the inside. See the below pics...

Post by **Orkney** » Thu Jan 24, 2008 10:11 am

Thats a pretty good way of doing it - never thought of that! keeps the heavy duty wires in the engine bay.

Post by **M_Temple** » Thu Jan 24, 2008 11:53 am

Thanks for the pics Lee - looks an ideal spot - as I said in my first post I wanted to keep the wiring in the engine bay and have the key access in the car interior, just as you have done.
Is it in the earth or 'live' wiring to the solenoid from the battery?

Post by **bmcecosse** » Thu Jan 24, 2008 12:28 pm

Don't fuse the ammeter lead!

Post by **M_Temple** » Thu Jan 24, 2008 12:54 pm

.... and the reason would be? I know if it blew it would disable the car, but I'd rather carry a spare fuse than use the fire extinguisher. Presumably the fuse would have gone for a reason.
I understand one of the main issues with an ammeter is the 30A cable transiting the bulkhead, so it seems sensible to put in some safeguard.

Post by **bmcecosse** » Thu Jan 24, 2008 1:42 pm

Because that' s your 'main feed' - if it blows - bang, you lose everything - especially worrying if it's nightime - lights all go out and the car grinds to a halt in the middle of the Motorway!!!!!!!!
Better just fuse the individual circuits. I would say if you really 'must' fuse it - then go for something like 100 amps! And yes - the main ammeter cables must be v well protected to ensure no chance of a short on them. Many instead fit battery condition meter which I don't like - and my Traveller has a proper ammeter!

Post by **MoggyTech** » Thu Jan 24, 2008 5:55 pm

and the reason would be?

If the fuse fails an alternator will be destroyed in a nano second, not a problem with dynamos though. But again you are fusing the main feed, and if the fuse fails, you lose all power to everything. Fuses will sometimes fail for no reason (usually a poor connection to the fuse itself).

Post by **bmcecosse** » Thu Jan 24, 2008 9:46 pm

Good point about the alternator - depending what causes the fuse to blow, the alt will either be feeding into the dead short (which will soon kill it) , or feeding into your light bulbs etc and with no battery 'sink' the volts will go sky high, the bulb filaments will overheat and stretch (they may not fail right away - but will do soon after) and the alternator will be damaged. They are NEVER to be run with the battery disconnected - which would be the situation if that 'main' fuse let go.

Post by **M_Temple** » Wed Jan 30, 2008 12:45 pm

Thanks for all the input - very, very useful and educational.
I now have a good location for the switch that keeps all the high amp wiring in the engine bay, but leaves the key accessible from the passenger compartment, and I will be protecting the ammeter leads with a good grommet and not a fuse!

I propose to put the switch in the battery to solenoid lead, unless anyone wants to tell me why it should be the earth side.

Post by **bmcecosse** » Wed Jan 30, 2008 1:55 pm

No special reason - just that's where they usually go - your way will be fine. But as 'crossword' points out in another thread - it's much safer to be working on the earth lead side of the battery. At least - take the earth off while doing the work on the +ve side!