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WJC56
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Joined: 22 May 2018
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Location: Burrum Heads, Qld

PostPosted: Wed May 23, 2018 3:57 pm    Post subject: Reverse polarity Reply with quote

Hello, I just took delivery of a MM SII Pickup. The seller tells me that the previous owner reversed the polarity on the car. Can someone explain what I need to do/change to put it back to original setup. Many Thanks, Bill (Burrum Heads, Qld).


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John Ballard
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PostPosted: Wed May 23, 2018 6:30 pm    Post subject: Reply with quote

Why would you what to?? modern radios for one need to be Negative earth.



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WJC56
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PostPosted: Wed May 23, 2018 7:44 pm    Post subject: Reply with quote

Thanks for the reply. With my full restoration, I want to be true to having it a true original rebuild.


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craigb
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Joined: 07 Apr 2018
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PostPosted: Wed May 23, 2018 7:49 pm    Post subject: Reply with quote

Early English cars often had positive to earth and according to my manual yours would have been too. I'm not sure why. One of the problems is that if you want to fit a radio, most are from after cars were all negative to earth and you can't fit them - been there and that in my first car at 16 and destroyed a radio! The easiest way around that is to reverse the polarity on the car and that's what may have happened to yours. Does it have a radio? I'm not an auto electrician so you might want to double check anything i say, but to my knowledge all you have to do is swap the leads on the battery and you will need to reverse the polarity on the generator. I'm sure if you google 'reverse polarity of generator' it will describe in detail but from memory to go positive to negative earth you would earth the generator to a battery and then touch a wire to one of the terminals for just a second or so. If you had an ameter that would need to have terminals reversed. Why did you want to change if it is working?



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craigb
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PostPosted: Wed May 23, 2018 7:52 pm    Post subject: Reply with quote

I missed the posts in between. If it is totally original and no radio, and no ammeter - then it is just swap the terminals and repolarise the generator - I think!



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John Ballard
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PostPosted: Wed May 23, 2018 8:07 pm    Post subject: Reply with quote

I have read that the reason British car builders had the bodies of their cars positive with the idea that a "electrically live " bodies would not rust.

Didn't work did it??? Eye Rolls



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craigb
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PostPosted: Wed May 23, 2018 8:44 pm    Post subject: Reply with quote

Thanks John - That's hilarious, I love it! My new favourite fun fact! You would think there is some science in it for them to do this and of course most rust is caused by mud traps holding moisture against bodies - unless it is an Alfa and i have heard from an ex York Motors Adelaide employee that they would send new cars straight off to a crash shop to be rectified because they were rusting already. They believed they had rust before they put paint on and was the steel they used. Makes me think of Peter Brock's 'divorce' with Holdens over that polarizer. All interesting car history though and thankyou.



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Monk
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PostPosted: Thu May 24, 2018 6:41 pm    Post subject: Reply with quote

Craig

I can remember people sending any new cars in Adelaide off to have fish oil sprayed in every imaginable orifice to stop them rusting. Not sure that it worked. Used to destroy the new car smell.

Seriously Bill, if your car has had the polarity reversed it will make pretty much everything simpler, as John and others have said.

Here's a thread from a couple of years back that sets out the positive to negative process: http://www.morrisdownunder.com/forum/viewtopic.php?t=4919

And this is the process, positive to negative:

Step 1 Disconnect battery. Turn it around so that the negative terminal is aligned with the earth strap to the body. Leave disconnected

Step 2 Reverse the ammeter connections. Electric clocks, rev counters and the like may be a problem with polarity so seek advice from
auto electricians if you have these fitted.

Step 3 Swap the leads on the coil, these leads will be marks SW & CB or (+) & (-).

Step 4 Fuel pump, heater fan and wipers are generally not polarity sensitive and therefore should run as normal

Step 5 If a radio is already fitted and is not a valve type, which is not affected by polarity, then change the polarity switch at the back, if fitted to
negative earth. If the radio is a positive earth type then you may have to change one that is negative earth.

Step 6 Change polarity of a generator :-
a) Disconnect leads on regulator "F" and "D"
b) Connect the battery, positive to starter negative to body
c) Stoke the field terminal wire "F" lead across the main battery feed terminal, marked "A" on the regulator. Do this about 5 times at one second intervals creating a spark each time. This will reverse the polarity of the dynamo or generator and is called "Flashing the Poles"
d) Reconnect the "F" & "D" leads to the regulator
e) Start the engine and check the ammeter is indicating the generator is charging correctly

There's a bit to turning back the clocks and you may have some unintended effects on accessories like a radio, as Craig has said. Basically, it needs to be isolated from any metal contact to earth, otherwise you'll cook it!

Cheers,

David



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DON58VAN
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PostPosted: Fri May 25, 2018 5:33 pm    Post subject: Reply with quote

If you go with positive earth, you will have to be very careful if you install a power socket for electronic accessories for items like a GPS navigator. Like the advice about radios, there is a real risk of destroying the accessories.

I think that this is an area where originality can easily be discarded. After all, the difference between +ve and -ve earth is invisible to the observer--unlike twin carbs or an alternator.



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WJC56
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Joined: 22 May 2018
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Location: Burrum Heads, Qld

PostPosted: Fri May 25, 2018 6:57 pm    Post subject: Reply with quote

Hello David, this is fantastic information. I appreciate you taking the time to provide the excellent step by step instructions to me. Kind regards, Bill


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Monk
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PostPosted: Sun May 27, 2018 10:21 am    Post subject: Reply with quote

Hi Bill,

Credit where credit's due, they were actually cut and pasted from Don's post on the earlier thread, so Don is the expert here. I did it once, probably following Don's earlier advice!

Cheers,

David



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