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MG TD TF 1500 - Battery disconnect switch?

Electricians help please.

On a positive gound car should I put the battery disconnect switch on the negative or positive cable?

Does it make a difference?


David
David

On our TF its on the negative cable.
Paul

It depends on the switch you've got.

Usual DIY "greenknob" battery-mounted switches are made smaller to fit the smaller negative terminal (but nothing a big hammer can't fix to fit it on the +ve ground terminal).

Ideally, chassis-mounted "big red cornchip" switches should be made to switch the LIVE cable (ie not ground) and take your starter motor out of circuit.
Will

I mounted a battery disconnect switch to a bracket attached to the Tube (Scuttle Hoop ??)just under the center of the dash board. It shuts off the negative side of the system (positive ground car). It is out of the way and unseen, but very easy to turn off or on. We have gotten into the habit of turning it off every time we shut off the ignition, just for added safety and security. The Green twist knob type would necessitate opening the bonnet each time you wanted the security of turning it off..

SPW
Steve

I've fitted a battery cut off switch to my Lotus Elan Sprint.

Being a fibre glass body I was concerned about electrical fires

I have fitted the switch in the live lead close to the battery. That means I will not melt my spanners if I short a terminal to earth whilst doing a service.


Jan T
Jan Targosz

I agree with Jan and Steve.
My switch is fitted in the glove box, out of sight and always at hand.
I also have the habit of turning it off every time I shut off the ignition and I always check before I start working on the car.

MGreetings

Erik
erik van hardeveld

I would go counter to the collective intelligence and break the earth connection. Few cars are as easily hot wired as the T series, and anyone attempting to do so would generally just jumper the hot side and be off in seconds. They probably wouldn't even realise that you had tried to prevent theft by placing the switch in the hot side. They wouldn't even need a heavy jumper if they cranked or bump started the car.
George B.

George,
The battery is so accessible (and thus the terminals) that fitting an isolating switch as an anti theft measure isn't too effective.

Read somewhere recently - could have been in the bulletin that a good theft protection is to make up a set of plug leads with very prominent numbers. Trick is though - put the numbers on the wrong leads. When you leave the car swop the leads over so everything looks OK. If anyone tries to start the car, even by hot wiring, the engine wont fire and they would not suspect the leads since the numbers would look correct.


Jan T
Jan Targosz

Actually, a Denver boot is the most effective deterent.
George B.

My 2cents....
I run a removable batt. kill switch and a "hidden" kill switch on the fuel pump. The batt switch for safety....the fuel switch ..well if you get her started your not going to get far with no fuel pump...maybe just far enough to end up in a really stupid and obvious place!
Cheers,
David 55 TF 1500
David Sheward

George,
"a Denver boot is the most effective deterent."....
Disassembley and storage in 5 different locations..(basement / dinning room...ect)... worked well for me last year!
David
David

Like David, I have my TD dismantled and the parts spread all over the house, garage and a few garden sheds. This should be the most effective anti-theft measure. The only thing is that last night I could not find my tie rod ends. They must have been stolen! So much for that theory.
Tony
Tony Cove

Yeh, I've lost headlight buckets, doors, windshields and genuine Lucas parts still in their boxes from my barn.
George B.

As to the fuel shutoff switch: if I were hot wiring a T series, all the work would be done under the bonnet and my shunt would go from the battery to the fuel pump and then to the coil; I wouldn't even know about your deterent.
George B.

At curbside checkin at Orlando airport using airport transfers sevenoaks last month, a person left their car unattended. The tow truck was there in a couple minutes, lowered a plate steel plate to the ground, and backed up sliding it under the tires, put on one strap, and drove away with car in tow. Took about one minute! Kill switch no help here! The average car theif in this area can pop the lock on older GM cars, Camrys, and some Hondas in 15 seconds and drive away. They would have no clue how to or desire to steal an MG. I have the green knob thing, which I undo when parked mainly due to the unfused circuits/fire risk- gotta keep the smoke in, etc.!
George Butz

Going back to the original question, I do not see why it should matter whether you cut off on the ground or the hot (positive) side. I do not understand Jan's comment that cutting off the ground line would make one prone to melting spanners. Even if you shorted the negative terminal direct to the car body, if the battery's ground line is cut, there is no circuit. Am I correct?
Rick Greenberg

Whoops, I meant the hot (negative) side.
Rick Greenberg

Rick,

Thanks for your response. Yes, the question was "does it make any difference to switch the positive or negative side of the battery in a positive ground car".

The general response seems to be that it makes no difference.

Thanks, Dave
David

It does make a difference; but it depends on your purpose. I have mine on the negative terminal, positive ground system. So if I work on any electrical components I just unscrew the terminal and kill the power. If I had it on the positive terminal and disconnected it to work on the electrical the battery would still be in the circuit, so say I put a wrench on the starter pole and the wrench touched the car frame I would complete the circuit and as Jan says "melt a spanner". If you only want to prevent battery drain it doesn't matter.
D F Sexton

If you disconnect ether side of the battery the battery is out of the electrical loop. Shorting a spanner against the starter lug to the frame will not spark if there is no connection from the frame to the battery. OR HAVE I MISSED THE POINT?
Jay Dyck

SOP for doing electrical work on all cars is to disconnect the earth first to prevent a spanner being used on the non-earth terminal from contacting the frame. For this reason alone the isolating the earth is preferable.
George B.

George B. has it right.
Blake J.

I see your point. Boy was I dull. You’re saying when you disconnect the battery, you need to take the wire off the post that is connected to the frame because if you took the wire off the other post and slipped and hit the frame you would take a lesson in welding.
Thanks for your info.
I am from the Show Me State
Jay Dyck

OK, now I feel better. I have a cut-off switch on my ground (Positive) cable, on each of my cars (TD and Magnette). I use it to cut power when working on the car and when I won't be driving for a while. It helps keep the battery charged and will make the clock last longer!
Rick Greenberg

This thread was discussed between 19/11/2002 and 22/11/2002

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