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MG TD TF 1500 - Positive vs. negative ground

Hi All,

I've searched the archives and seen that some people have been converting from positive to negative ground, and that the main reasons for doing so are changing the charging system or setting things up for a modern radio.

One thing I was going to do with mine is put a pertronix electronic ignition in. I've been so happy with my electronic ignition in my '68 midget that I thought I would do the same with the TD.

Pertronix makes positive ground EI units, so that isn't an issue. However, if I ever decided to switch, I would need a different unit.

Any thoughts on going one way over the other?

Thanks,
Scott
Ocelot

Ocelot,
Leave the inexpensive points in,,,, then change your ground to whichever you want !!!

SPW
Steve Wincze

If you ever want to change to an alternator (for obvious reasons) you will need to change the ground.

John
John Redman

Scott - Either positive ground or negative ground work equally well. That said, if there is no pressing reason to switch to negative ground, leave it as is and tell everyone you believe in purity of origin (or any other BS reason you want to), it is after all original. If you have a particular reason to make the change (such as installing a modern radio, which can't be heard when at speed, or a CD or DVD) then go ahead and make the change, it is not all that difficult. Regarding the Pertronix ignition, I am in favor if it (this from one who was stranded by a vehicle due to electronic ignition), it is easy to install, is reasonable priced and ends any kind of problems with worn distributor bushings. I installed it in our MGB and have another unit to install in the TD when I get some time (by the way, having been stranded once by a Hall effect ignition, like the pertronix, I do carry a spare backing plate complete with condenser and pre set points just in case). Cheers - Dave
David DuBois

Scott,
I run Neg ground. Car was "partly" transfered when purchased so I finished the job. I also did some mods to my "eletricks", adding some extra fusing & switching to the system. IMHO, I just feel safer that way. Years ago I had an Austin burn to the ground in a rainstorm when the headlamps shorted. Had that one been neg grnd it would not have happened! Also a big fan of the pertonix (like Dave I do carry a set of pre-set points as aback-up). The car starts much easier whith the pertronix and I would rather spend the time driving than setting points! Just put another pertronix in my wife's new toy 2 days ago (a 73 Opel GT) noticed a big improvement in starting there as well!
Cheers,
David 55 TF1500 #7427
David Sheward

How is negative ground safer than positive wrt headlights shorting? I would think it shouldn't matter at all wrt headlights shorting.

Scott
Ocelot

David - I have to disagree that you would not have had a problem had your Austin ben wired negative ground. Regardless of the polarity, if a wire shorts to ground, there will be a maximum of current flowing for however long it takes for the wire to act as a fuse. I will agree that if you had converted to negative ground AND added fuses at the same time, you would have avoided an incenerated car, but that would have been because of the fuses rather than the polarity of the vehicle.

By the way Scott, if you do install the pertronix ignition, you will have to readjust the distributor as the timing point will be change somewhat. I would suggest that before installing the pertronix, that you roll the engine over and set it right at the point where the points are just about to open, then after installation, readjust the distributor to again get same point with the pertronix (it is read the same way, either with a meter or a test light. Cheers - Dave
David DuBois

David,
You are, of course, quite right...what I should have said was "I somehow feel safer"...having the potential for a short confined to hot wires in a harness and switchable instead of the whole car being the "plus" side.
The austin headlamp "hot" jumped to a wet ground wire from the rain. A day I will never forget...."hey anybody in here driving a little green car in the parking lot?....it just burst into flames!"
You betcha ...I fuse my headlamps now!
Cheers,
David 55 TF1500 #7427
David Sheward

While we're on the subject of positive vs. negative earth.....

This might seem like a really silly question....but in the event one needs to "jump" a positive earth vehicle...like mine...can you hook the cables up from a negatively grounded automobile ...like my other car...by just doing the standard negative to negative and positive to positive connections??

Thanks!

Jim
Jim Rice

Jim - Yes, you can just hook things up positive to positive and negative to negative. Just be very careful that you don't get confused when hooking things up and that the cars are not touching, say at the bumpers, when you do it. Cheers - Dave
David DuBois

I believe there is no need to convert to negative ground. I have a modern CD player hidden, with equalizer, an alarm, amplifier, all running from a phantom-negative ground which coexists with the original. The only problem is that you may need a positive lead which comes up when you turn the ignition key, which can be easily supplied by a rele.

Denis
1950 TD
Denis L. Baggi

This thread was discussed between 09/02/2005 and 26/02/2005

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