Classic cars forum & vehicle restoration.
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Luegolover
Joined: 02 Mar 2017 Posts: 15 Location: London
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Posted: Sun Mar 11, 2018 9:40 pm Post subject: Positive or negative earth? |
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I am rebuilding my Healey 100 and having completed the inner bodywork I am starting to put all the mechanicals together and having finished the suspension I am turning my attention to getting the engine, wiring and fuelling installed. And so I am starting to ponder the wiring and specifically the earthing.
I have a kit to rebuild my fuel pump and a that would clearly be +ve earth. However a part of me thinks that I should fit an alternator which would, I presume, be negative earth.
So, do I can my fuel pump and buy an electronic pump that works on both +ve & -ve or do I ditch the alternator idea?
Are there any other considerations? |
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ukdave2002
Joined: 23 Nov 2007 Posts: 4127 Location: South Cheshire
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Posted: Sun Mar 11, 2018 10:17 pm Post subject: |
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I'm presuming it's an SU fuel pump? As long as it doesn't have an electronic points conversion, then the pump is dual polarity.
If it has a diode across the points this will need to be reversed, or simply removed, they were never fitted originally.
Dave |
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jp928
Joined: 07 Jun 2016 Posts: 249 Location: Australia
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Posted: Mon Mar 12, 2018 12:31 am Post subject: |
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If you do go neg earth (recommended due to no of accessories that would then be available to you), dont forget the ignition - some systems, coil especially, are polarity sensitive . I once sold a Rover that I thought ran very sweetly. Week later the buyer rang and said it was running roughly - What have you done? Nothing....well not much - swapped it to neg earth so could fit a modern radio. Swap the low tension leads on the coil please.
If your coil is marked + and - on the turret, make sure they are correctly connected.
jp 26 Rover 9 |
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lowdrag
Joined: 10 Apr 2009 Posts: 1586 Location: Le Mans
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Posted: Mon Mar 12, 2018 7:37 am Post subject: |
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ukdave2002 wrote: | I'm presuming it's an SU fuel pump? As long as it doesn't have an electronic points conversion, then the pump is dual polarity.
If it has a diode across the points this will need to be reversed, or simply removed, they were never fitted originally.
Dave |
I helped someone out with my spare SU pump who had broken down and he sent me a new replacement. The new ones are automatic. Plug and play comes to mind. Obviously an alternator and negative earth is the way to go these days what with satnav, phones and ipod etc. i regret keeping mine positive earth when I rebuilt her but can't be bothered now to change it. If I did I'd surely go for one of these:-
http://www.powerlite-units.com/about-dynalites/ |
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ukdave2002
Joined: 23 Nov 2007 Posts: 4127 Location: South Cheshire
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Posted: Mon Mar 12, 2018 10:34 am Post subject: |
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lowdrag wrote: | ukdave2002 wrote: | I'm presuming it's an SU fuel pump? As long as it doesn't have an electronic points conversion, then the pump is dual polarity.
If it has a diode across the points this will need to be reversed, or simply removed, they were never fitted originally.
Dave |
I helped someone out with my spare SU pump who had broken down and he sent me a new replacement. The new ones are automatic. Plug and play comes to mind. |
The original SU pumps are not polarity sensitive, it was only when SU added a zener diode across the points (too prolong points life) did the pump become polarity sensitive. Its a simple matter to determine if the pump has a diode as its visible with the cap removed, if the polarity is to be changed ; simply turn the diode round or take it out completely.
The pump on the right has a diode, the pump on the left has a capacitor, (capacitors were also used to prolong points life) the capacitors are not polarity sensitive.
The diodes and capacitors have no effect on the working of the pump, so can be added to old pumps or removed from newer ones....
Dave |
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Luegolover
Joined: 02 Mar 2017 Posts: 15 Location: London
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Posted: Tue Mar 13, 2018 9:44 pm Post subject: |
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Thank you for your feedback and pictures. I don't know what the fuel pump is so will dig it out at the weekend. I suspect it is from 1954 though and so I doubt it has a diode, looks way to modern for the pump from memory. |
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