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View Full Version : What's the down side of "positive ground system"?



Lukens
09-01-2012, 08:36 AM
Looking at several TR3s. Like the title: what's the down side?

JodyFKerr
09-01-2012, 08:38 AM
If you plan on keeping everything stock, then you're fine.

If you want to start upgrading/adding electrical components you'll likely have to switch to negative earth.

TR4nut
09-01-2012, 12:27 PM
If you ever run a Garmin, and accidently ground the case, you will find you'll need a new Garmin.

TR3driver
09-01-2012, 12:57 PM
And if you ever let anyone else work on it, there's a good chance they won't notice the positive ground. Hooking up the jumper cables backwards can lead to all sorts of unpleasant things, including a battery explosion.

A better question might be : What's the up side?

Geo Hahn
09-01-2012, 03:12 PM
I've kept both of mine positive earth just because that seems like part of the character of the car. Certainly not an upside, just a preference.

It has been easy to leave as is since I have nothing that demands the output of an alternator or a negative ground current source and no one else ever works on the car.

I do have utility sockets (aka cigarette lighters) hidden below the dash that are wired to accomodate negative ground devices (e.g. air compressor).

Since you are 'looking' and a new member here, I'll mention: It is the work of a few moments to switch the car from positive ground to negative ground or vice versa so which configuration a vehicle has may be of little consequence in your buying decision.

FordFiesta
09-01-2012, 05:31 PM
One potential upside:

When the government (state or federal) or your ever-greedy insurance company wants to put a "black box" on your Triumph to keep tabs on you or your driving habits, they won't be looking for positive ground and their electronics will be toast. Sounds paranoid, I know, but ten years from now it'll be "normal".

Extra points if you drive something like a Model A Ford, that's both positive ground AND 6-volts!

I believe also that I read long ago (in "Old Cars Magazine" or somewhere similar) that there is a slight technical advantage to positive ground - something to do with the direction of electron flow through the points and condenser making those components function better. Probably nothing that really matters, though positive grounding was normal in the USA as well as the UK for many years.

TomMull
09-01-2012, 06:30 PM
If you want to start upgrading/adding electrical components you'll likely have to switch to negative earth.

Radios and such were always always an issue. Mine has a positive ground radio which, by the way, I cannot and never could hear with the engine above an idle (perhaps it doesn't work?). I've wondered about the motorcycles I've heard with the radios competing with the pipes.
I figure that if I need a GPS in my TR3, I don't need a TR3. I'll stick with my positive earth like the British stick to driving on the left.
Tom

glemon
09-02-2012, 01:49 AM
There was a rumor floating around at one time that negative ground might be slightly more rust resistant, something about electrolysis or the flow of electrons or something, don't know if there was anything to it.

I converted most of my positive ground cars to negative just so I could run a more modern radio. But if you aren't going to do anything with modern electrical accesories no reason to change imho.

As stated it is quick and easy to switch polarity, I have done it on several cars and gone back to original on a few, never a glitch.

Worst issue I had is when I tried to wire and isolate a negative ground stereo in a positive ground MGB (many many years ago, I will add). Ended up with lots of burnt wire and smoke, somehow didn't fry the radio though.

TR3driver
09-02-2012, 05:05 AM
Worst issue I had is when I tried to wire and isolate a negative ground stereo in a positive ground MGB (many many years ago, I will add). Ended up with lots of burnt wire and smoke, somehow didn't fry the radio though.
Long time ago, a friend and I took a 3000 mile road trip, he in his MGA & I in my TR3A. To stay in touch during the trip, we both temporarily installed CB radios. He clamped the antenna onto the back bumper, wired positive to positive and away we went.

2nd day on the road, his dash suddenly erupted in smoke. Fortunately he had left the battery cover and one battery clamp loose, so it only took a few seconds to disconnect the battery. Sure did make a mess out of the wiring under the hood, though!

Obvious in retrospect, but neither of us realized it beforehand ... his CB had the antenna clamp grounded to the negative lead. Apparently, it had worked at first because the bumper mounts were so rusty that they didn't conduct; eventually the vibration must have lead to a good connection and formed a dead short through the antenna shield. The radio had a fuse, but of course it was in the "hot" lead so didn't blow.

That was a fun trip! We picked apart the bundle of fused wires, robbed a wire from somewhere (wiper motor IIRC, who needs those) to power the coil, and continued on.