Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Converting to Negative ground

Wanting to convert my TC from positive to negative ground I've watched the John Twist video which just states arc between terminals A and F on the regulator/control box. However no mention is made of the coil or the ammeter which I read elsewhere appears to state that both those should have the cables reversed. Plus an article regarding a positive rather than a negative spark at the points can affect performance. Am I reading to much and making things to complicated. I have a standard dynamo but will be using LEDs and including a satnav for touring. No electronic ignition and standard SU fuel pump.
JK Mazgaj

The leads must be reversed on the ammeter for it to read correctly. The coil will function without reversing the leads but it will perform better by switching the leads.
L E D LaVerne

Hello JK, John Twist is right, but he's just telling you of one of the ways to convert your dynamo to be a negative ground system. There's one other absolute that must be done - switch your battery connections. Anything after, what is done is for convenience, or consistency. You don't have to swap your ammeter's wires, but it makes life simpler. You don't have to swap your coil primary wires, but it makes your spark happier. It's much easier to buy LED devices that are intended for negative ground connections. The archives of this BBS are full of discussions about converting to negative ground/earth systems and devices. They're well worth searching out. Bud
Bud Krueger

Is there a downside, other than lacking 'originality', to converting to negative ground? I'll confess to occasionally being slightly befuddled by positive ground, although I rationally know I shouldn't be.

There are actually upsides to converting.

More negative ground LEDs are available, of course there are bi-polarity, but cost an arm, and 2 legs.

I have heard of dwell meters reading the opposite, I.e. instead of reading the period the points are closed they read the period they are open. Which of course, if you are aware is no big deal.

But, each to their own, mine is negative ground, longest part of the procedure is repositions the battery so that the connections reach.

I flash the field directly from the positive battery terminal AFTER switching the battery around. After it worked, I disconnected the ground side if the battery and reversed the ammeter and coil.

The Brits were using positive ground while the US was trying to start cars with 6volts. I had. 6volt car once, I had to use a lighter to see if the headlamps were on.

P G Gilvarry

Thanks all for the pointers. Will be all easy to do during the rebuild. Happy New Year and here's to some healthy driving in 2022.
JK Mazgaj

Brittrix, Ltd ( sells LED inserts for most classic British cars in polarity neutral design. They don't care whether you have a vehicle with positive or negative ground (earth). 26 different LED light boards which cover over 350 different vehicle models.
Lew Palmer

It is rarely mentioned because of their rarity but still worth mentioning. If you have an original radio that is positive earth it will be toast if you change polarity.
W A Chasser

I have seen some very old radios that had a small plug on the side that allowed them to be converted negative earth or positive earth.
John Quilter (TD8986)

Mine was German, Blaupunkpt, 6/12volt, negative/positive earth, the very first trans-gender radio.

And,it played music too.
P G Gilvarry

This thread was discussed between 31/12/2021 and 02/01/2022

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.