mk1-forum.net

Posted: **Tue Mar 10, 2020 10:39 pm**

Thinking of putting a car back to positive earth.

It has the old Smiths tacho so I guess that will be fine as the leaflet with it shows both earth alternatives. I'll have to reflash too - so that the polarities are correct.

Nothing brings to mind that is potentially a problem - but any thoughts welcome please? Anything I may have overlooked???

Posted: **Wed Mar 11, 2020 12:00 am**

I did my ‘67 S back to +ve, no real problems.

Has to be dynamo not alternator [but you can get +ve dynamators as an alternative].

Make sure the gauge voltage stabiliser is conventional bi-metallic, not replaced by a modern integrated circuit regulator which is polarity sensitive.

Swap the SW and CB [+ and -] low tension wires on the coil, so the ignition has the correct ground return path for the HT.

Obviously use no modern LED lamps anywhere.

If you have twin tanks, need to change the battery else the terminals will be too close to the tank when you rotate it 180°

If you have electric fuel pump, make sure it’s the points polarity-insensitive version, not the later solid state replacement.

Posted: **Wed Mar 11, 2020 7:52 am**

I always thought positive earth cars were more prone to rust than negative . Why change?

Posted: **Wed Mar 11, 2020 8:31 am**

You must change the contact set in the distributor
The metal transfer on the points is reversed usually failing after a few hundred miles
It happened a lot in the 70s when people were fitting -ve earth radios

Posted: **Wed Mar 11, 2020 10:49 am**

Hmmm radios didn't come to mind, though I doubt if I'll ever fit one.

Its a twin tank and didn't consider the battery either - will need to check that.

Thanks for some useful answers - I have a little more thinking to do. New points for example

Posted: **Wed Mar 11, 2020 11:09 am**

Check that your SU fuel pump will work with reversed polarity. With regards to a radio. We used to fit negative earth ones into a wooden box to isolate the radio chassis from body earth.

Posted: **Wed Mar 11, 2020 11:22 am**

whistler wrote: ↑Wed Mar 11, 2020 11:09 am Check that your SU fuel pump will work with reversed polarity. With regards to a radio. We used to fit negative earth ones into a wooden box to isolate the radio chassis from body earth.

I vaguely recall that wooden work around!! This is the car that came from City Motor Company in Cardiff btw

Pump will be new, but will definitely check.

Thanks

Posted: **Wed Mar 11, 2020 12:46 pm**

I'm still on positive, found an FM radio no problem and have used LED bulbs here there and everywhere except headlights (you need all the spare Amps you can get for the heater fan, sealed beams and wipers!!!)

Posted: **Wed Mar 11, 2020 12:51 pm**

JohnA wrote: ↑Wed Mar 11, 2020 8:31 am You must change the contact set in the distributor
The metal transfer on the points is reversed usually failing after a few miles

So if material was building a point on one side of the points, after the polarity swap the material would transfer the other direction? Interesting.

To the OP, if the car today is negative earth what is your reason for wanting to convert back to positive? Is it a question of originality?

A general overview of polarity conversion can be found in the Mini Mania tech article linked below.
https://www.minimania.com/Electrical_polarity

Posted: **Wed Mar 11, 2020 5:06 pm**

Back in the day, when going from positive to negative, all we did was change battery terminals - connect the earth and tap the positive terminal on battery three times !!
Dont ask why three times, but it always worked no problems

Posted: **Wed Mar 11, 2020 6:19 pm**

AndyPen wrote: ↑Wed Mar 11, 2020 11:22 am
whistler wrote: ↑Wed Mar 11, 2020 11:09 am Check that your SU fuel pump will work with reversed polarity. With regards to a radio. We used to fit negative earth ones into a wooden box to isolate the radio chassis from body earth.
I vaguely recall that wooden work around!! This is the car that came from City Motor Company in Cardiff btw

Pump will be new, but will definitely check.

Thanks

I worked there in the Parts Department around 1970/72.

Posted: **Wed Mar 11, 2020 10:15 pm**

Originality is the main reason I guess, plus at 124 inches I think my cable may be a little short to cut again... so can always buy a new cable if there's a good reason to stay negative

Can anyone comment on the rusting mentioned? I seem to vaguely recall hearing that's one reason why everything became neg earth???

Whistler, the car was sold there in 64 mate

Posted: **Thu Mar 12, 2020 1:12 pm**

I have seen the positive ground rust argument posted on message boards multiple times. I have no idea if it is true or how to provide supporting documentation (pro or con).

The one reason I can offer for leaving the car negative ground is the argument that has been around for years... compatibility with modern cars and accessories. Consider that one day your Mini may need a jump start. Well intentioned friends who don't know or suspect your car is different may make incorrect connections between the cars causing damage to both. And of course, any accessories you add to the car are easier to come by with negative ground.

Over he years I have seen both positive and negative ground "stickers" applied near the battery to warn people about polarity that may be different from what is expected.

Again, either ground will work and the decision is largely based on what you want more than any technical arguments.

Posted: **Thu Mar 12, 2020 2:00 pm**

dklawson wrote: ↑Thu Mar 12, 2020 1:12 pm I have seen the positive ground rust argument posted on message boards multiple times. I have no idea if it is true or how to provide supporting documentation (pro or con).

The one reason I can offer for leaving the car negative ground is the argument that has been around for years... compatibility with modern cars and accessories. Consider that one day your Mini may need a jump start. Well intentioned friends who don't know or suspect your car is different may make incorrect connections between the cars causing damage to both. And of course, any accessories you add to the car are easier to come by with negative ground.

Over he years I have seen both positive and negative ground "stickers" applied near the battery to warn people about polarity that may be different from what is expected.

Again, either ground will work and the decision is largely based on what you want more than any technical arguments.

I recall hearing the theory that corrosion is slightly encouraged by positive earth but no idea on the science of that.

I've only ever seen warnings that "this vehicle is wired negative earth" although as pointed out above a warning about positive earth would be far more relevant these days.

Posted: **Thu Mar 12, 2020 5:04 pm**

IslandBlue wrote: ↑Thu Mar 12, 2020 2:00 pm I've only ever seen warnings that "this vehicle is wired negative earth" although as pointed out above a warning about positive earth would be far more relevant these days.

We have the positive earth warning stickers available through U.S. vendors like Britishwiring.com (link below)
https://www.britishwiring.com/Positive- ... /st172.htm

Posted: **Thu Mar 12, 2020 5:20 pm**

IslandBlue wrote: ↑Thu Mar 12, 2020 2:00 pmI've only ever seen warnings that "this vehicle is wired negative earth" although as pointed out above a warning about positive earth would be far more relevant these days.

I’ve got these on my car - one on the boot floor next to the battery, and one on the front slam panel.

Posted: **Thu Mar 12, 2020 10:30 pm**

I hope mine will look as nice as that one day

Decided to buy some new battery cable and put the fittings on once I have made up my mind - indecision is a wonderful thing

Posted: **Fri Mar 13, 2020 6:42 pm**

iain1967s wrote: ↑Thu Mar 12, 2020 5:20 pm
IslandBlue wrote: ↑Thu Mar 12, 2020 2:00 pmI've only ever seen warnings that "this vehicle is wired negative earth" although as pointed out above a warning about positive earth would be far more relevant these days.
I’ve got these on my car - one on the boot floor next to the battery, and one on the front slam panel.

That's interesting although I have a feeling that I'd subconsciously read that as negative earth!

Posted: **Fri Mar 13, 2020 7:36 pm**

IslandBlue wrote: ↑Fri Mar 13, 2020 6:42 pmThat's interesting although I have a feeling that I'd subconsciously read that as negative earth!

However, the label isn't really there for you. It is there for those who own the car after you or Good Samaritans who want to help you jump start your car's engine.

Posted: **Fri Mar 13, 2020 10:38 pm**

dklawson wrote: ↑Fri Mar 13, 2020 7:36 pm
IslandBlue wrote: ↑Fri Mar 13, 2020 6:42 pmThat's interesting although I have a feeling that I'd subconsciously read that as negative earth!
However, the label isn't really there for you. It is there for those who own the car after you or Good Samaritans who want to help you jump start your car's engine.

That's kind of what I meant, if I saw that label on a car that wasn't mine I might "recognise" it without reading it because at a glance it looks similar. Sounds daft but that's human nature, we sometimes see what we expect to see irrespective of whether it actually is....

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Positive earth - any drawbacks?

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Re: Positive earth - any drawbacks?

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