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MG TD TF 1500 - Battery Switch

I would like to add a battery kill switch to the negative (ground) side. Because I have a period accessory Bell cover over the battery I cant use the normal ones with the wheel. I just bought a switch at radio shack that says 50 amps 12 vdc. My question is, if I am running it through the ground side of battery, would I need big amps, or would I be safe? This was not meant for car battery.

Keith
K E MURPHY

Your switch needs to be able to handle full battery current plus overload such as when jumpstarting or charging... I would think at least 150% over battery amperage...
Geoffrey M Baker

I am with Geoffrey, go big or stay at home. Cheers - Dave
D W DuBois

Keith,
As Dave and Geoffrey state "go big or stay at home"
even those little green ones are not that good,, sure they work for a while, but they get pitted easily,, go with a regular race car type switch,,

SPW
SPW Wincze

Don't forget the huge current drawn by the starter motor. Bud
Bud Krueger

All the little electrons that go out of the positive post ultimately must go back in through the negative post. It's a zero sum closed system. Back in '65 or '66 they tried to teach us something about the sum of the amps in a circuit but I don't think it stuck.

Jud
J K Chapin

Thanks for the info, I will take the cheap switch back to Radio Shack. I had this sneaky suspicion that I wasn't going to get by that easy! Now to figure how to use the big switch I saw at auto store, without it looking bad on my 8 years restoration. I also plan to put cigarette receptacle in car for phone charging etc, not really a lighter. Should be no problem right? Have to figure where to hit a good ground. If I get that, then I have to figure how to hook up this thing I have for my other British car (DeLorean) that keeps the clock and radio settings when battery is disconnected.
K E MURPHY

Hi Keith: I thought Deloreans were made in New Brunswick (just north of Maine -- not just south of Newark)... Peter
Peter Pope

You can wire a modern 12v power receptacle to the acc plugs on your dash...
Geoffrey M Baker

Is the DeLorean the regular or time travel model? If the latter, that could sure help clear up points of originality! George
George Butz

DeLoreans were built in Northern Ireland using sources from all over Europe and the US. It had to do with a 100 million pound government grant to create jobs...
Geoffrey M Baker

For a negative earth (ground) system hooking up an accessory socket is pretty easy and the thing can be located about anywhere. Most devices that you might hook up to it draw relatively small amounts of current so about any convenient source of hot and grounding to about any metal should work. If in doubt check continuity and resistance from the intended ground point to the neg. post on your battery - Should be very low to almost nonexistent resistance. Be sure it's really a negative earth system before hooking up a device and many will self destruct if hooked up to the wrong polarity.

Jud
J K Chapin

Here's a photo of my switch (just in front of the fuel pump)which is pull cable operated from under the dash (the red cable)which has the advantage of not having to cut big holes in the bulkhead and the heavy duty cabling is very short. The disadvantage is you have to open the bonnet to reset it manually. The cable connections are covered in rubber, put together with superglue.
Regards
Declan


D Burns

Second photo.


D Burns

Declan, what is the gauge for? Seems you've got a lot of pipe there I don't have :)
Geoffrey M Baker

Thanks for the photos Declan, but mine is one of those TFs that you need the dexterity of a monkey to work on --and no fuel pump under the bonnet.
K E MURPHY

Geoffrey,
The gauge was just a temporary installation to measure the inlet manifold pressure when I installed the PCV valve to reduce the oil leaks last year. FYI it registered -700mbar at idle and without a piece of a cigarette butt in the line as a damper, the needle nearly self destructed..

Regards
Declan
D Burns

This thread was discussed between 29/05/2014 and 30/05/2014

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