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MG MGB Technical - isolation switch for battery

Hi Guys, having put my new battery under the bonnet, everything working good, just kept it as positive earth, no problems, I would like to fit an isolation switch, does it matter which cable it goes on, ie: can I put it on the positive cable to earth (car body) or does it have to go on the Negative cable going to Starter switch?

Cheers Jack.

ps: would it be wise to change the black cable going to earth from the positive end of the battery to red cable, so that people realise that although it is going to earth it is still the positive from battery?

cheers Jack.
Jack New Forest

I've put in an isolation switch, I do not know if there is an incorrect way, but I put it on the 'earth' side for convenience. In effect, if there is no ground, then all stops ( or does not go!) Mike
J.M. Doust

Installing the on/off switch in the ground cable is the simplest and most effective method of shutting off all power from the battery. A red cable, running to the grounding point, would be a good idea in your situation. RAY
rjm RAY

Isolation wise it doesn't matter which wire a switch is in, however if you need to work on the 12v terminal connector but not the earth connector you always have to disconnect the earth first, so it makes more sense to put it in that wire to begin with.

I'll add my vote to a red cable, or red sheathing over the cable on the +ve.
PaulH Solihull

My vote is earth cable. I think if you put in other side, and inadvertently earth that negative terminal, (eg when tinkering with spanner, something falling on it, etc), then you better call the fire brigade!
But if isolated on the earth side, accidentally earthing either terminal does nothing.
Graham M V

Hi Guys, just thought I would show the finished job of my isolation switch and changeover to 12V under the bonnet, just got to paint that small bracket, looks crap bare metal.

Cheers Jack.

Jack New Forest

different image

Jack New Forest

Good job Jack. My only concern, and it is just a minor point is the final earth connection, is it 'earth' enough if you see what I mean? The inner wing may rust, even at that point. The other thought, why not have the cut out switch more accessible? ie in the car with you, so that within seconds you could 'throw' it? Like the cut out switch of motorcycles, easy to hand when all electrics need cutting off? Just a thought. Mike
J.M. Doust

I would also think that running the earth cable to the engine block would provide a much better path for the battery ground. RAY
rjm RAY

This thread was discussed between 12/02/2012 and 17/02/2012

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