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MG TD TF 1500 - Battery History Question

Greetings to all!

Out of ignorance, my interest, and due to a question asked me, could someone give me a quick historyof MG T-series6-volt (if ever) and conversion to 12-volt system?

Thanks for the schooling,


Jerry Chandler 1951 TD

If you have 51 TD & 54 TF ...they should both be 12 volt positive ground systems unless they have been converted to negative ground.
David Sheward

I believe the TA had twin six volt batteries under the rear floor, over the rear axle, much like the MGA and MGB. This design provided plenty of amperage, helped weight distribution and handling, and lowered the center of gravity. I'm not sure about the TB. The TC, TD, and TF had a single, 12 volt battery wired with positive ground up front in the engine compartment.
D. Sander

David thanks. My '51 TD is 12-volt NEGATIVE ground and the "54 TF is positive ground. But, when/if did a manufacturing change occur?


Jerry Chandler 1951 TD

Your 51 TD was converted by a PO. My 50 TD still has positive ground.
Mort Resnicoff (50 TD-Mobius)

US manufacturers switched from 6 to 12 volt and standardized to negative ground in the 1950s. Ford went to 12 volt, negative ground in 1956, GM and Chrysler I think in 55. Chrysler started using alternators in 1960.
MG was always 12 volt, but switched to negative ground in 1968, also the first year they used alternators.
D. Sander

Well hey there fellows, while we are on the subject, my 51 TD came to me in pieces (which it pretty much still is.) Is there anyway to determine if it was ever converted to negative ground? What will happen if I hook it up bass akwards? Thanking yooz. Sandman
smb brainsky

Without wiring it is hard to tell. The generator needs to be polarized. That's about it. If the wiring is in, then the polarity of the ammeter and the coil would have to be switched.
D. Sander

Geez David, there isn't a wire on this car. It has been stripped clean. All I have is a very original looking replacement harness. I realized early on that the wiring will be my biggest challenge here. Electrical is by far my weakest skill. I have nothing to follow here and I would like to do it right. When the time arises, expect to see many threads here from me. I will owe you all many drinks. Thanks again and cherio. Sandman
smb brainsky

SMB - As David S. stated, the only thing you can do is to hook up the battery whichever polarity you want the car to be (positive ground for originality or negative ground for modern convenience) then polarize the generator to match.

For the record, MGs were 12 volts from the original M types. The pre war cars were negative ground. They changed to positive ground with the TA (thinking that positive ground would retard corrosion - didn't work) and went back to negative ground in late 1966 or early 1967. Cheers - Dave
Daved DuBois

In a few very short months, you will be able to discuss your TD rebuild and electrical questions in person with other TD owners at British By The Sea 2013,,, June 2nd,, we usually have over 25 TD-TF's in attendence,,,, all willing to share their experiences,,



smb, track down the correct wiring diagram for your car (ie dash dimming, floor dimming w/ or w/o turns, etc). There are some color printed and coded ones out there somewhere. Believe it or not, installing the harness is mostly straight forward. Vast knowledge here on the board here, stuff like David DuBois article on ground preparation, etc., etc. Search around in the archives. George
George Butz

A follow-up thank you to ALL the MG T-Series brothers" for your comments. I was not energetic enough, intelligent enough, etc, to retort an army buddy of mine from the sixties, that he was certain there had been an evolutionary conversion from 6 to 12. He is a "gear-head" for mostly U S muscle cars, anyway!

Appreciation to ALL,


Jerry Chandler 1951 TD

I wonder if Sandman could put his dynamo in a bench vise, rig up an electric motor and fan belt (or even a highspeed electric drill) to spin it in the correct direction and use a voltmeter to determine its polarity?
J K Chapin

Wouldn't have to, Jud. Just put a jumper between the two terminals, hook up an analog voltmeter on a low scale between the jumpers and the body of the dynamo and give the pulley a sharp twist, The direction of the deflection of the needle will show the polarity. If the positive lead (+) is connected to the body and the negative lead (-) is connected to the terminals the meter will deflect upward (on scale) for a positive ground generator. A negative ground generator would have the deflect downward, i.e., below zero. It's also quite likely that there won't be any meter reading. Bud
Bud Krueger

Hi all. It is no need to polerize the generator before all the harness is connected and the car is ready to be started.
Good luck.
Thoralf. Norway TD4490
Thoralf Sorensen (TD4490)

Ah yes, this promises to be a very interesting project.Thank you all for your support. I feel braver already.
Steve, I have been to BBTS the last 2 years. A really great time. Terific people. Talking to T people 2 years ago, a fellow overheard and promptly went to his car and came back with a set of Whitworth wrenches. Told me he was looking to pass them on to someone who needs them. I was so excited that I had my girlfriend hug him for me. Honestly, I think it is the people that make this a great hobby. I will keep an eye out for your car this June. Can't wait. Hope to meet you.
Bud I can try that on my generator now. I will post my results.
Cheerio. Sandman
smb brainsky

Almost forgot - turn the pulley clockwise. Bud
Bud Krueger

"It's also quite likely that there won't be any meter reading. Bud"

Because of a bad generator or a poor test?

Thanks. Jud
J K Chapin

Either, Jud. The brushes in the generator may be stuck and not be making contact with the commutator. The pole pieces may have lost magnetization. Etc. Bud
Bud Krueger

Bud "The pole pieces may have lost magnetization"
Not very likley, ever had a screw driver that was magnetized lose it's magnetization? Just doesn't happen. Once those molecules get arrainged together they stay that way.
Bob Jeffers

Daved, You are a knowledgeable MG man but M-types were 6 volt. I have one and 6 volt batteries are costly and a nuisance!.
Barry Bahnisch

This thread was discussed between 18/02/2013 and 20/02/2013

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