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Positive to Negative Earth ?
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Bob T



Joined: 16 Nov 2010
Posts: 128
Location: Sudbury, Suffolk

PostPosted: Mon Sep 26, 2011 10:21 pm    Post subject: Positive to Negative Earth ? Reply with quote

Hi,
I have just bought a 1955 Austin A50 which is positive earth, as manufactured.
I have found a company that do electronic conversions for Lucas DM2 dizzys as fitted to my car, but they claim that they only work on negative earth cars.
I am confused, logic says they are selling something for which there is no market, but I am sure that is not so.
Is it possible to change the earth polarity?

Cheers
Bob
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Nic Jarman



Joined: 05 Oct 2008
Posts: 1031
Location: Stoke by Clare, Suffolk

PostPosted: Mon Sep 26, 2011 10:53 pm    Post subject: Reply with quote

I would assume the DM2 was fitted to negative earth cars too.
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1973 MGB roadster
1977 MG Midget 1500
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MVPeters



Joined: 28 Aug 2008
Posts: 822
Location: Northern MA, USA

PostPosted: Tue Sep 27, 2011 2:20 am    Post subject: Reply with quote

There's nothing polarity-sensitive about a conventional Lucas distributor.

If you want to convert the car to negative earth, remove/replace the radio & most clocks.
Replace the electric SU fuel pump (for some reason I've never understood) if there is one.
Reverse the ammeter &/or voltmeter wires if they are fitted.
The fuel gauge should be fine.

Just reverse the coil low-tension wires & re-polarize the dynamo & you'll have a negative-earth car.

Then you can add whatever negative-earth accessories you wish - including electronic ignition systems, some of which are available in a positive-earth version, by the way.


PS PM sent about the wipers!

PPS & reverse the battery connections! You'll probably need new cable terminals.

PPPS - 3rd edit! Do a Forum Search for >> positive negative conversion << There's lots of individual messages. Apparently the SU fuel pumps work either way (I did say I didn't understand!.
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2002 MINI Cooper 'S'
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