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Wales
by Joske Vermeule, September 1
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Forums39
Topics49,911
Posts838,143
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Jun 14th, 2026
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Joined: Oct 2015
Posts: 25
Just Getting Started
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OP
Just Getting Started
Joined: Oct 2015
Posts: 25 |
Is the M3W electrical system positive or negative ground? I remember a lot of British autos were positive ground when most American & German cars were negative ground, which made things a bit confusing to work on, but I don't know if this is still an issue. My friend had a '59 MGA that used two six volt batteries to make up a twelve volt system...
Bill in FtL
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Joined: Oct 2013
Posts: 6,723 Likes: 2
Talk Morgan Sage
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Talk Morgan Sage
Joined: Oct 2013
Posts: 6,723 Likes: 2 |
Worldwide convention dictates Negative (-ve) Earth since those dark days..
Steve
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Joined: Nov 2013
Posts: 1,947
Talk Morgan Enthusiast
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Talk Morgan Enthusiast
Joined: Nov 2013
Posts: 1,947 |
In the days of dynamos before alternators you could change the polarity. I did it on a Hillman Imp to fit an electric oil pressure gauge
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Joined: Jul 2011
Posts: 3,643
Talk Morgan Addict
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Talk Morgan Addict
Joined: Jul 2011
Posts: 3,643 |
I seem to remember having to push the contact in the regulator for a coupe of seconds to make the switch from positive to negative earth. I may have remember incorrectly, however I do remember it only taking a few minutes to make the change over. The radio was changed over by an qualified auto electrician.
Ian
2011 Plus 4
Wild Mogs Reims 2019, Goodwood 2018, Isle of Man 2017, Carried on to Caramulo" 2016
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Joined: Dec 2008
Posts: 22,371 Likes: 354
Roadster Guru Member of the Inner Circle
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Roadster Guru Member of the Inner Circle
Joined: Dec 2008
Posts: 22,371 Likes: 354 |
You had to spark one of the leads onto a particular spot on the regulator to repolarise a coil, but I can't remember the detail.
DaveW
'05 Red Roadster S1
'16 Yellow (Not the only) Narrow AR GDI Plus 4
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Joined: Oct 2015
Posts: 25
Just Getting Started
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OP
Just Getting Started
Joined: Oct 2015
Posts: 25 |
I'm not sure if British electrics were similar, but I remember polarizing the regulator on my 6-volt VW by touching the B+ output terminal on the regulator to the charge indicator light terminal with a screwdriver. Hard to believe it's been 45 years!
Bill in FtL
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Joined: Jul 2011
Posts: 3,643
Talk Morgan Addict
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Talk Morgan Addict
Joined: Jul 2011
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I did it on an Triumph Herald, and that too was about 45 years ago. I must be getting old.
Ian
2011 Plus 4
Wild Mogs Reims 2019, Goodwood 2018, Isle of Man 2017, Carried on to Caramulo" 2016
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Joined: May 2014
Posts: 367 Likes: 2
Learner Plates Off!
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Learner Plates Off!
Joined: May 2014
Posts: 367 Likes: 2 |
Our M3W's are -ve earth.
Most (if not all) modern vehicles are -ve earth because +ve earth leads to very rapid electrolytic corrosion.
I know this from experience because many years ago I fitted a Lucas 12V dc. car dynamo to a Vincent motorcycle combination that I owned at the time, and the dynamo had been polarised for +ve earth. The aluminium parts of the bike (of which there were many) very quickly grew a film of white powder and I was advised this was because it was +ve earth.
I re-polarised the dynamo and reversed the battery connections and the corrosion was no longer a problem.
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