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PostPosted: Sun May 06, 2018 5:39 pm 
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Location: East Fife.
Car Model: SAAB 96/MGB/Twingo/Niss Figaro
A friend of mine's 70s classic recently had an electrical problem while driving, smoke coming from under the dash. By the time he'd stopped the car, gotten into the battery to disconnect it, the loom behind the dash was smoked. He could have lost the car.
This got me thinking.
I have a battery isolater on the negative battery terminal, but am wondering now if I should have some sort of isolation switch in the cab, that's accessible from the drivers seat.

Has anyone fitted such a switch?
If so, did you route the main battery earth line through the switch, or just the main grey feed line that goes from the alternator up to the fuse box?
Where did you mount the switch?
Any thoughts would be appreciated.

The Troll.


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PostPosted: Mon May 07, 2018 7:18 pm 
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Location: REMAINING UNFAITHFUL TO FACTORY STANDARD SPECIFICATIONS SINCE 1988
Car Model: OLD SAABS....NUMEROUS
HELLO ANDY,IF YOU MEAN THE ' AUTOLEC' TYPE?
THEN YES,INTERRUPT THE GREY ALTERNATOR WIRE ,AS WELL AS THE MAIN RED BATTERY FEED,THROUGH THE 'AUTOLEC' SWITCH.
SPEND THE MONEY ON GENUINE ' AUTOLEC' SWITCH,WITH SEPERATE SPADE TERMINALS,ON THE REAR( USE THESE FOR THE GREY ALTERNATOR WIRE)

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PostPosted: Thu May 10, 2018 2:14 pm 
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If you don't isolate the alt it will carry on running. Also carry a motorsport spec hand held fire extinguisher.


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PostPosted: Fri May 11, 2018 11:19 am 
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Location: East Fife.
Car Model: SAAB 96/MGB/Twingo/Niss Figaro
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I carry 2 fire extinguishers, though I'm not sure they're rally spec.....

If I started smelling smoke, I would immediately cut the engine, (which would stop the alternator turning), and then would want to cut the main feed line that either goes from the starting motor, up to the alternator, or the alternator to the "always live" part of the fuse box. If I'm not mistaken, that would kill all the electrics of the car.

Not sure I'd like to be bring the circa 100 amp cable that goes from the battery, to the starting motor, into the car....

Andy


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PostPosted: Fri May 11, 2018 6:29 pm 
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Location: REMAINING UNFAITHFUL TO FACTORY STANDARD SPECIFICATIONS SINCE 1988
Car Model: OLD SAABS....NUMEROUS
HELLO ANDY,

IT'S NOT DIFFICULT TO DO,SIMPLY RUN A LENGTH OF 'TWIN' BATTERY CABLE,THROUGH THE BULKHEAD,YOU WILL NEED TO DRILL A 25MM HOLE,AND UTILISE A THICK RUBBER GROMMET TO INSULATE.......OR,THERE ARE PLASTIC 'INSULATION CONNECTORS' THAT WILL PASS CURRENT 'VIA' EITHER SIDE ,THE BULK HEAD HOLE,IF YOU DON'T WAN'T TO RUN THE CABLES THROUGH?

YOU COULD FIT THE AUTOLEC 'OUT OF SIGHT' INSIDE THE GLOVEBOX,IF YOU MAKE A SUBSTANTIAL BRACKET,TO FIX TO THE INNER BULKHEAD?

WHAT 'RALLY V4' (RICHARD) IS SAYING,IS THAT IF YOU DO NOT ALSO RUN,THE THICK GREY ALTERNATOR CABLE,TO THE REAR OF THE 'AUTOLEC' KILL SWITCH,THEN THE ENGINE WILL CONTINUE RUNNING ON THE 'ALTERNATOR CHARGE',EVEN WHEN YOU HAVE,INTERRUPTED THE 'BATTERY' SUPPLY.......

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PostPosted: Mon May 14, 2018 3:57 pm 
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Andy stick a £4 smoke alarm under the bonnet :wink:

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PostPosted: Thu May 17, 2018 8:35 am 
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Location: East Fife.
Car Model: SAAB 96/MGB/Twingo/Niss Figaro
Jools.
Perhaps I'm missing something.....

If you put a switch in the line (line 74, 4 mm2, if you have the wiring diagram) between the alternator, and the first 4 fuses (always live), on the fuse box, then no power goes from THAT fuse box connection to connection 30 on the ignition switch. Therefore there can be no power at terminal 15 of the ignition switch, which gives power to the coil. ie the engine can't run.....
Anyway, as I've said, if there was any smell of burning, the first thing I'd do is kill the ignition. The problem with that is there are a whole lot of circuits on the car that are still live, even with the ignition off. This was the problem my mate had. Killing the ignition, stopped the engine, but his short circuit was somewhere in the "always live" part of the loom.
By the time he got to the battery, and got the terminal off, the wiring loom, behind the dashboard, was toasted.

ps Chris. Smoke detector under the bonnet wouldn't have done much.
His short circuit was behind the dashboard. HIS NOSE was the smoke detector, ha ha ha :D

Andy


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PostPosted: Sat May 19, 2018 6:28 am 
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Location: REMAINING UNFAITHFUL TO FACTORY STANDARD SPECIFICATIONS SINCE 1988
Car Model: OLD SAABS....NUMEROUS
MORNING ANDY,NOT SURE WHAT YOU ARE TRYING TO DO HERE ?

IF YOU WAN'T ALL THE ELECTRICS TO BE 'DEAD' SUCH THAT A 'FIRE' SITUATION CANNOT ARISE,WHILST THE CAR IS NOT IN USE ? YOU MUST INTERRUPT THE 'LIVE' BATTERY CABLE.

THE ONLY CURRENT THEN REMAINING,WILL BE FROM THE BATTERY,TO THE REAR OF THE 'AUTOLEC' SWITCH,ONCE THE 'RED' KEY IS REMOVED...OF WHICH,YOU COULD STILL GET A 'POTENTIAL' ISSUE/FIRE RISK ?

TO ALLEVIATE,ANY 'ISSUE' OF THIS ON MY CLARION 99T,I HAVE ALSO A' DIS-CARNECT' DEVICE FITTED,ON THE 'POSITIVE' SIDE OF THE BATTERY POST ITSELF,WHICH IS SIMPLY A FEW TWISTS OF THE PLASTIC KNOB,TO BREAK THE CIRCUIT(BETWEEN BATTERY /AUTOLEC)IF THE CAR IS IN STORAGE.....

https://www.demon-tweeks.co.uk/performa ... out-switch

https://www.amazon.co.uk/Battery-Isolat ... B01ARMC5K8


Attachments:
CONTROL CENTRE.jpg
CONTROL CENTRE.jpg [ 57.54 KiB | Viewed 396 times ]
YOU MUST INTERRUPT AND SWITCH THIS GREY WIRE.JPG
YOU MUST INTERRUPT AND SWITCH THIS GREY WIRE.JPG [ 41.04 KiB | Viewed 396 times ]
BONNET SHUT,TO SHOW ALL ROUND CLEARANCE OF BATTERY AND TRAY.......jpg
BONNET SHUT,TO SHOW ALL ROUND CLEARANCE OF BATTERY AND TRAY.......jpg [ 55.23 KiB | Viewed 396 times ]

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PostPosted: Sat May 19, 2018 9:10 am 
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Surely the correct solution is to put a suitably-rated fuse in-line with any unprotected cables? Years ago my Mini 1275GT, which had previously been owned by a muppet with far more DIY enthusiasm than sense (and, I was stunned to find out, was an electrician), suffered an electrical failure while driving along due to an uninsulated connector touching the metalwork behind the instrument panel. Luckily I had a junior hacksaw in the boot, which I used to cut the earth strap on the battery. I had to strip out almost the entire loom because the main feed from the alternator had been glowing bright orange.

I don't know what the maximum draw on that cable would be on a 96 but whatever it is, it will take much, much more current to cause a fire so if, for example, it would never expect to see more than 40A in normal operation, fit a 40A fuse and in the event of a short it will definitely blow. Even if you aren't in the car at the time to flick a switch, the car will protect itself. 40A is probably about the most a 4mm2 cable would be rated at, and probably less.

The nearer to the battery (alternator in this case) that you put the fuse, the better to protect the maximum length of cable from being pinched or chafed. In theory you can do the same with the main battery feed, although you'd need a very big fuse and you'd also need to work out the maximum current you need to feed to the starter on the coldest of cold starts.

Modern cars have umpteen fuses. My Mini had only two - one for everything on the ignition-live circuit and another for everything on the permanent-live circuit. However, the feed from the alternator to the fuse-box was unprotected.

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PostPosted: Sat May 19, 2018 5:00 pm 
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Location: East Fife.
Car Model: SAAB 96/MGB/Twingo/Niss Figaro
Jools
This is not to do with power to the electrics, when the car is not in use. I already have the battery isolator that you gave a link to in your post. (Amazon).

This is to do with cutting power to the car electrics , from the drivers seat, when you are driving. The problem my mate had was that by the time he stopped the car, killed the ignition, realised the problem was still present, got out the car, opened the bonnet, disconnected the battery, the wiring loom behind the dash was toast.

I think I'll either put a reasonably heavy duty switch in the line between the alternator, and the fuse box terminals 1 to 4, and/or maybe Bill's idea of a 40 amp in line fuse.
I'll hide the switch under the dash, but accessible from the driver's seat.
Perhaps mount it on the cross beam just below the light/fan switch.
Good anti theft devise as well......

Thanks to all who have contributed.

Andy


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PostPosted: Sat May 19, 2018 5:51 pm 
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Whether it's a fuse or a switch or both, you'll need to figure out the maximum current you'll expect that wire to carry in normal use. My guess at 40A really was just a guess.

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PostPosted: Sun May 20, 2018 12:47 pm 
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Location: East Fife.
Car Model: SAAB 96/MGB/Twingo/Niss Figaro
Bill
It'll need to be a pretty hefty switch, 40 amps sounds about correct to me.
The isolator switches I can see on some sites are good for 100 amps.

Unfortunately my multimeter can't read more than 10 amps, so hard for me to check what the normal current would be with everything, including main beam headlights and spots etc, on.
Andy


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PostPosted: Tue May 22, 2018 1:02 am 
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I was thinking about installing a 100A fuse terminal to our well known fibreglass tubbed car, once I saw the proximity of the starter motor red cable (unfused) to the chassis leg at the back. There already is a screw type isolator on the negative terminal. The notion of fusing the positive terminal was scoffed at by social media 'experts', so I haven't bothered. I still think it's a good idea, the challenge would be deciding on a fuse size large enough for starting the car, but small enough to provide meaningful protection in the event of a fault.

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PostPosted: Tue May 22, 2018 9:12 pm 
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Car Model: SAAB 96/MGB/Twingo/Niss Figaro
Doive

Not sure about fusing the main battery cable.
One of the problems with fusing all the power supply, is that if said fuse blew, (perhaps because it was faulty) in the middle of the night, when your bombing down the road, you suddenly lose all your lights.
I think that's why your headlights don't go through fuses on the standard set up.

I just want to be able to very quickly, without leaving the drivers seat, kill the power to all the electrics, should the need arise.

Andy


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