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Positive to negative earth pros and cons?
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Morepower



Joined: 15 Aug 2019
Posts: 6

PostPosted: Tue Aug 27, 2019 7:58 pm    Post subject: Positive to negative earth pros and cons? Reply with quote

Hi all
My DB18 Daimler Consort arrives Monday and am compiling a list of jobs and improvements to do, what do you guys think about swapping from positive earth to negative earth? I remember doing this to a mini many many moons ago and from what I recall it was quite easy. I am thinking of car radios and charging the phone whilst out in particular.

Thanks all

Graham
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ukdave2002



Joined: 23 Nov 2007
Posts: 3399
Location: South Cheshire

PostPosted: Tue Aug 27, 2019 8:46 pm    Post subject: Reply with quote

The only advantage is as you have identified; there are far more accessories for -ve earth....


Dave
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Phil - Nottingham



Joined: 01 Jan 2008
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PostPosted: Tue Aug 27, 2019 8:56 pm    Post subject: Reply with quote

I agree - if you use the old tech no need to bother. If not change but make sure you identify all existing polarity sensitive accessories
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alastairq



Joined: 14 Oct 2016
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PostPosted: Tue Aug 27, 2019 11:05 pm    Post subject: Reply with quote

I heard tell....that positive earth vehicles rot less than negative earth vehicles......?? Smile
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petelang



Joined: 21 May 2009
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Location: Nottingham

PostPosted: Tue Aug 27, 2019 11:33 pm    Post subject: Reply with quote

Important tip, if you change polarity, disconnect the Dynamo if you have one fitted, and then flash the field connection to the new positive battery terminal a few times. This resets the field and prevents potential problems with regulator points burning.
Peter
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Morepower



Joined: 15 Aug 2019
Posts: 6

PostPosted: Wed Aug 28, 2019 7:51 am    Post subject: Reply with quote

Thanks for your thoughts, I might go for it, if I remember correctly I have to:
Flash the dynamo (I might fit a dyanamotor)
Swap the coil leads around and swap the ammeter leads over

Have I forgotten anything?
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Bitumen Boy



Joined: 26 Jan 2012
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PostPosted: Wed Aug 28, 2019 11:19 pm    Post subject: Reply with quote

If there's a clock fitted I think that might be polarity sensitive.
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Penman



Joined: 23 Nov 2007
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Location: Lancashire

PostPosted: Wed Aug 28, 2019 11:28 pm    Post subject: Reply with quote

Hi
This might be stupid question but:
Would wipers try to start in the wrong direction from parked?
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roverdriver



Joined: 18 Oct 2008
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PostPosted: Thu Aug 29, 2019 8:24 am    Post subject: Reply with quote

Penman, I have done it on a couple of P4 Rovers that have an interesting operation for parking the wipers. They start, run and park as normal.
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alanb



Joined: 10 Sep 2012
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PostPosted: Thu Aug 29, 2019 9:35 am    Post subject: Reply with quote

Don't forget the fuel gauge,
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Phil - Nottingham



Joined: 01 Jan 2008
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PostPosted: Thu Aug 29, 2019 7:01 pm    Post subject: Reply with quote

Whether the fuel gauge needs changing over depends on its type - most do not whether stabilised or direct. Temp gauges no need but Voltmeters and Ammeters do, Clocks vary however as do electric fuel pumps
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Riley Blue



Joined: 18 Jun 2008
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PostPosted: Thu Aug 29, 2019 8:08 pm    Post subject: Reply with quote

Swapped over and fitted an alternator to my Riley and now the temperature gauge no longer works - neither does the fuel gauge, but it never has. I've now got lots more electricity, don't really know what to do with it all... Smile
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ukdave2002



Joined: 23 Nov 2007
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PostPosted: Thu Aug 29, 2019 10:03 pm    Post subject: Reply with quote

Phil - Nottingham wrote:
Whether the fuel gauge needs changing over depends on its type - most do not whether stabilised or direct. Temp gauges no need but Voltmeters and Ammeters do, Clocks vary however as do electric fuel pumps


If its an SU fuel pump and has a quencher diode, the diode simply requires reversing or removing completely, if it has electronic points either swap for the new polarity or use mechanical points.
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Ray White



Joined: 02 Dec 2014
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Location: Derby

PostPosted: Sat Sep 28, 2019 6:41 pm    Post subject: Reply with quote

If you don't have the information to hand, how do you know if something is polarity sensitive or not?

I am just thinking about the petrol tank sender unit I have just bought. The instructions show negative earth but I am hoping I can just swap the wires over for positive earth?
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Phil - Nottingham



Joined: 01 Jan 2008
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PostPosted: Mon Sep 30, 2019 10:15 pm    Post subject: Reply with quote

The petrol gauge will either work properly or not at all. This applies to most but some may work back to front.

If there are any modern "solid-state" components they may well be ruined
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