Quote from: Dave DND on September 07, 2017, 06:44:50 PM
Personally, I`m not a fan of messing with an earth, as if anything is powered then it will "look" for an earth if one is not present. You have seen lights that play silly buggers when an earth is poor as the voltage dissipates through anything that is connected if a strong earth is not present. I spend half my life repairing delicate electronics that have failed as voltages ripple the wrong way backfeeding through circuits, and with more and more electronic sophistication being added to our Buggys, Stereos, usb chargers, dashboards, LEDs, etc, then I feel that this has the potential to end in tears.

Kill the supplied voltage - not the earth

Have to agree with Dave on this one...

And the debate goes on.

Where the switch goes depends on what you are trying to achieve.  If it's a battery cut out switch to kill power to make the vehicle safe to work on or as a winter measure to stop the battery draining then it should IMHO be in the negative circuit on a negative earth car. Would positive work? Yes. Is it as safe? No.

If however you want a safety kill switch then yes put it in the positive circuit but you still risk damage to sensitive electronics if it's wired as has been sugested and the car is running when it's operated.

Just to say I agree with whoever achieves nothing.

I knew it wouldn`t be long before we had a radio in here suffering from an insufficient earth fault

This is what can happen when you have live voltages floating about and no earth for them. This was caused by a corroded ring terminal on the radio earth supply and it could not handle the radio supply voltage, which then finds a way to dissipate itself through any and all parts of the circuit board that it can.





Kill the Earth and this can happen - Kill the Positive and this can NEVER happen 

You kind of back up what I'm saying there Dave as the earth was not completely disconnected so electricity being what it is found its own path back.

I've seen a BMW alternator turned to scrap when the person jump starting it disconnected the positive terminal first.  Admittedly the cars battery was so flat it had forgot it was a battery.

Disconnecting the positive on a running engine fitted with an alternator is not good unless you have other safety measures wired in.  Some sort of Diode is needed I believe?

As I said what are you trying to achieve?  If it is a simple battery safety switch used for maintenance ECT then the best option is from the negative terminal as close to the battery as possible. 

If it's a safety kill switch you probably want it in the cockpit or even motor sport style on the outside BUT this means that you have a length of 'hot' wire and at least 1 terminal that is just waiting to be touched with a spanner.

Not wanting to be negative but disconnect the negative first.

Defo with the earth connected to the Kill switch - read loads about this on the forums both kit car , buggy builds and USA and all say safer to do Negative kill switch than positive

Back in my car hot-wiring days 

Rip off the steering column and start touching wires together to see what sparks and what turns the car over

If there is no voltage there, then there is nothing to play with 

Kill the supply voltage dead - clue is there also

We kill something DEAD not kill it LIVE

Just sayin . . . 

J   

Simple question:

What battery connection should you always disconnect 1st?

Anyone got a picture of the safety kill switch with the resistor (not a diode) that is designed to protect electronic ECU's etc?

A dual pole cut out switch will solve any problem.

Quote from: Flags on September 12, 2017, 06:08:16 PM
Simple question:

What battery connection should you always disconnect 1st?

Anyone got a picture of the safety kill switch with the resistor (not a diode) that is designed to protect electronic ECU's etc?

Not disagreeing that I would usually yank the earth lead first in disconnecting a battery, but then I would be doing that for safety, not security.

Depends I suppose on "WHY" you are disconnecting it.

Just a thought guys! if you wanted the switch as a safety cut out and you put it on the earth side. If you were in an accident and your engine was still running, perhaps revving its nuts off, you might get a shock when the engine carries on running after you had turned this switch off!!!

Rob

Quote from: DND Services Ltd on September 12, 2017, 05:44:04 PM
Back in my car hot-wiring days 

Rip off the steering column and start touching wires together to see what sparks and what turns the car over

If there is no voltage there, then there is nothing to play with 

Kill the supply voltage dead - clue is there also

We kill something DEAD not kill it LIVE

Just sayin . . . 

J   

Ha Dave.... thought I was the only car "hijacker" on the forum... Dare not say any more 

Quote from: farmer rob on September 12, 2017, 11:18:25 PM
Just a thought guys! if you wanted the switch as a safety cut out and you put it on the earth side. If you were in an accident and your engine was still running, perhaps revving its nuts off, you might get a shock when the engine carries on running after you had turned this switch off!!!

Rob

Yep already said that a safety cut out should be on the positive side but not wired as suggested.
I've given up on trying to post pictures on here but here is what I mean:

https://www.cliosport.net/attachments/batt_cut_1-gif.945703/

That works for me 

And seeing how this thread has gone, it leave me with only one question . . .

What is the best colour battery to have?      

Just a thought . . .

When we disconnect a battery on the car for working on it, 99% of us will disconnect the earth one. This is deep ingrained in our thoughts and we all seem to do it - but where did it come from?

It is because we are usually surrounded by a metal tub and any live wires could touch absolutely anything we are working on and cause issues, or is it because in the olden days when stories like this were formulated and handed down by our grandparents, that cars were positive earth, so what would have been the main feed to everything would have been the earth lead?

Vehicle polarities changed from positive earth to negative earth, but did the advice change with it?

I was taught to disconnect the earth first because if you disconnected the feed first there was a good chance the other end of your spanner could touch the body etc causing a dirty great flash.

I've always wired my buggies very simply. I've always put the isolator (usually a Durite red flag-key type) in the +ve feed main cable with a 10A line fuse in parallel with it to keep the clock/ radio memory fed. This fuse would just blow if any ne'er do well tryed to start it...no biggie. Low tech I know but that's the kind of guy I am...