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MG TD TF 1500 - Battery disconnect

There is a disconnect under the hood on the positive battery terminal. I want to move the battery disconnect under the dash for convenience sake instead.

My question: should I break the positive (ground) side, or would it be better to break the negative (hot) side.

This positive ground nonsense has me thinking a bit too hard.


My car is still positive ground, I ran the negative cable to a regular Kill Switch which I mounted on the "hoop" under the dash,, The switch is out of sight,, but at the same time, very easy to quickly turn off in an emergency.
Steve Wincze

I should have added that the switch is mounted at the center of the "Hoop" ahead of the shifter

Steve Wincze

I mounted mine as a cable operated switch so I don't have heavy duty cables all over the place.


D Burns

The chrome T-handle on the left of the steering wheel in the photo below operates the switch. The main advantage being short HD cable runs and I can kill the battery whether I'm in the car or when I want to work under the bonnet. The only disadvantage is that you have to open the bonnet to reset it but in the case of an emergency that is not an issue in my opinion.


D Burns

I'm thinking about the battery switch for safety and theft proofing. I might also hide a SPDT switch on the lead to the fuel pump with a warning light that'll go out when closed so i don't take off and then stall.

I often wonder about parking at a motel when on long trips, or even for lunch. Yes, most people are quite honest, but helping a kid go for a 2:00am joy ride isn't in my plans.

My REAL question is, why one side of the battery over the other?


You want to disconnect whichever side of the battery goes to ground, be it positive or negative.

That way, if you inadvertently touch the OTHER post or circuit on the other side of the battery to ground you won't have a completed circuit and subsequent short, welded wrench, smoke, fire and screams.

If you disconnect the non-grounded side it would still be possible to short the battery if you touch the post (or any connection before the disconnect switch in the circuit) and the ground (anything connected to the chassis of the car).

I hope that's clear.

It is the same reason you always disconnect the grounded side of the battery first when removing the battery.
David Littlefield

Clearly that's the safest way.

I'm also wondering about electrolytic effects and corrosion, leaving either a pos or neg charge on the whole vehicle while it's seeking to close the circuit.


"I'm thinking about the battery switch for safety and theft proofing. I might also hide a SPDT switch on the lead to the fuel pump with a warning light that'll go out when closed so i don't take off and then stall."

If you don't have a spot light, there is a free switch on the far right side of the dash that can be wired into the power line to the fuel pump. I did that when I restored the car. A couple of years later I allowed our son to take the TD to the prom. He was all decked out in a tux and drove off, on the top of the world, only to walk back from a short way down the road, completely crest fallen and said the car died on him. I knew immediately what had happened, walked back with him to the car, turned the switch and sent him on his way. The next day, I removed the switch from the fuel pump.

Let's face it, there is an exceedingly small chance of a kid taking the car for a joy ride. First of all, kids today not only do not want a car like our T series cars, they couldn't figure out how to even get the car started and if they did, they would then be confronted with that strange thing called a shift lever that doesn't have a P,D,R, etc on it and if they ever figured out, they would never figure out the secret of the flyaway parking brake.

If somebody really wanted the car and could figure out the flyaway hand brake, whey will load it on a trailer and silently drive away with it. We drive our TD all the time and never think a thing about leaving it in a hotel parking lot (we do try to park it close to the main entrance) and have never had any incidents of attempted theft or even any vandalism. The biggest problem is the looky lous who want to ask a million questions when we are trying to get our luggage into the car and be on our way. Cheers - Dave

DW DuBois

To your original question. As I understand it the Ground (Earth) side of the battery is usually switched. Exactly why I am not sure... I think it is because it is easier and when the ground is interrupted it definitely opens the circuit. I just use one of the ones that goes on the battery post, and usually only disconnect when stored for over a couple of weeks. As Dave says... I have never had someone "monkey" with the TD when parked. Theft deterrent is the manual transmission and the lack of labelling on the switches and the parking brake.
... CR
C.R. Tyrell

I mounted mine in the glove box. The wall is strong enough to hold it with no issues. Been there 5 years now. In front is a double throw switch for the fuel pumps. Up is for the main pump under the hood, down is for the axillary in line pump in the rear under the tub and the center is off.

All mostly hidden by various junk I seem to accumulate in the glove box.

Please no comments on the glove box. Photo was taken many years ago and it looks a little better now.


Mort 50 TD

Mike, as has been said, disabling the circuit by opening the ground leg avoids the arcing and sparking when tools (or cables) contact ground. I use a simple disconnect on the ground terminal (-) that has a large green knob on the disconnect screw. It's easy to take the knob out and take it with you when you leave the car if it makes you feel more secure. Bud
Bud Krueger

This thread was discussed between 28/07/2015 and 31/07/2015

MG TD TF 1500 index

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