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Positive or negative earth?

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Luegolover Avatar
Luegolover Steve L
London, London, UK   GBR
I am rebuilding my car 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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RAC68 Avatar
RAC68 Raymond Carbone
NJ, Jersey Shore, USA   USA
Steve,

As I see it, it depends on what you intend to do in the future. When I decided to switch to negative ground, I planned to install an alternator (which also gets rid of the regulator problems) and a sound system I could really hear. Since all good sound systems and alternators easily available in the USA are designed for negative ground, my decision was maid. Additionally, along with the in-line fuses I have added to each circuit, I have also added 3 relays to control head and driving lights to reduce the demand on my original ageing harness wiring to a fraction of the load it original called upon to carry. keep in mind that when you flip the headlight switch, power for the headlights passes through the headlight switch and low/high beam switch as well as through the harness. With the installation of the relays and addition of a separate harness from the alternator, only the demand for switching the relays is now passing through my original harness while power to operate the lights is traveling through a much heavier harness directly form the alternator. Although changes like these could possibly be done with positive ground circuits, it is much easier to achieve (component acquisition and Help response) when dealing in a negative ground installation.

As for your fuel pump. I am still using my original SU fuel pump and have a points unit that could be used on either grounding approaches. I have added a Transill to extend the life of my points indefinitely as it sends to ground all but 24 Volts (needed to clean corrosion from the tungsten points) of the close to 200 volts induced by the action of the pump's coil. However, you may have an electronic or other SU model that would require replacement. I would check with the pump manufacturer before changing anything.

As with all my modifications except in-line fuses, all can be reasonably easily removed with original components and brought back to full concourse qualification.

Ray(64BJ8P1)



Edited 1 time(s). Last edit at 2018-03-17 06:36 AM by RAC68.

MarkBD Avatar
MarkBD Mark D
LLandassillio, West Wales, UK   GBR
Steve,
I went to negative earth but i used an alternator that looks like a dynamo as i wanted to try and keep the overall look, these alternators are available in both polarities if you want to stay with positive earth, i would recommend going neg earth this will give you more options for the future such as halogen head lights. Original fuel pump will work on both polarities, just make sure you swap the battery leads and coil leads over and you run a cable of suitable amp rating from the alternator to the battery, i ran mine to the battery side of the starter solenoid. I went to a single battery when i did my upgrade.

Mark (1954-BN1)

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RAC68 Avatar
RAC68 Raymond Carbone
NJ, Jersey Shore, USA   USA
Steve,

Not quite aware of what is available in the UK, however, I chose converting to a neg-ground not only to install a number of easily available add-ons but the cost and difficulty of road-trip repair was also a consideration. I do like the alternator Mark has chosen, but a commonly available 65 amp Delco Alternator provided reliable amperage along with a built in regulator at a very reasonable price. Since I have no interest in maintaining concourse qualification but do want to retain the original Healey image throughout, I have found ways to install modern units either incognito or with minimal (from my perspective) eye disruption. The attached pictures provide 2 examples. The first is the installation of a full sound system installed in a vertical console created to accept the head and equalizer/amplifier of an Acura TL system. The second and third are the installation of the Delco alternator. keep in mind that all original components have been saved and are available for reasonably easy reinstall if I ever desire to return to concourse qualification.

Hope this helps,
Ray(64BJ8P1)


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Michael S Avatar
Michael S Michael Salter
Dwight, ON, Canada   CAN
Steve, as Ray said, "As I see it, it depends on what you intend to do in the future."

I have a different take on the subject of modifications such as alternators etc.
I feel that these cars are a part of our heritage and as such every attempt should be made to retain them in their original condition.
I completed the restoration of my first Healey in 1979 when you could still still buy many of the parts at your local BLMC dealer. Over the years I have owned, repaired, modified and restored dozens of Healeys including a 100S and over that time I have learned one very important lesson.

THE BEST WAY TO RUIN A CAR IS TO EXTENSIVELY MODIFY IT

I have had customers spend thousands of $ doing every sort of modification that you could imagine including many myself (check here): AHX12 build
Even that car, AHX12, is now in the process of being restored to original.

Stick to the original. The engineers who designed and developed the Healey actually did know what they were doing and had the advantage of testing on thousands of cars (by their customers) to perfect the breed. Certainly they didn't have the benefit of modern technology but what they produced was very reliable and easy to service.

The only visible modifications I have on my current (concours gold) Healey are a 3rd brake light (because the originals are often missed by gawkers) and a hidden digital volt meter which incorporates some USB ports for my GPS and phone charger, and they can be removed completely in about 30 seconds.

As I say "If you want a Ferrari buy a Ferrari because no amount of money will turn a Healey into one".

Just my opinion.



Michael Salter
Technical Chairman (Big Healeys)
Austin Healey Concours Committee

Luegolover Avatar
Luegolover Steve L
London, London, UK   GBR
Thank you all for the replies. I was in a little bit of a muddle with my thoughts on this so it has helped.

I am not interested in having a concours car but I do want to retain the original look of the car and so I am not sure I could cope with a modern looking alternator, I can imagine now that every time I raised the bonnet at a car event I would find myself cringing at the sight of it. I am pleased to discover the petrol pump can run both polarities so that is good news. I am also pleased to discover that the alternators in a dynamo body are available in both polarities (feel a little silly for not looking into that before I posted). However, including taxes that runs out at about £600 which is eye watering so I will put that on the back burner for a while.

My only other query is if I do go for the alternator what other modifications to the standard wiring loom do I have to do?

MarkBD Avatar
MarkBD Mark D
LLandassillio, West Wales, UK   GBR
Steve
I used a C45 Dynamator ,45 Amp alternator (dynamo Look alike), i paid around £160 and has been fitted for 2 years with no problems. There is a small amount of rewiring involved, i have all the details with diagram available if you let me have your email details.

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MarkBD Avatar
MarkBD Mark D
LLandassillio, West Wales, UK   GBR
Luegolover Avatar
Luegolover Steve L
London, London, UK   GBR
Hello Mark,

That looks perfect. A definite. It also requires negative earth so I guess that is the decider.

Thanks
Steve

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PAN Avatar
PAN Alwyn Keepence
Ipswich, Queensland, Australia   AUS
Michael, you are a man after my own heart!
Alwyn

Graham3647 Avatar
Graham3647 Graham Carpenter
Hereford, Herefordshire, UK   GBR
Hello Mark,

I tried a C40 dynamo which was supplied as a C45, obviously it wouldn’t fit so I went for an alternator.
Only found out about the mix up some time later.
Cheers,
Graham.

thodav Avatar
thodav Thomas Davis
Owings Mills, MD, USA   USA
Greetings
I installed a one wire gm type alternator that I bought from JEGS. I wanted my charge indicator light to work so I purchased a low voltage warning lamp kit that turns the charge light on if voltage drops below 11v. https://www.americanautowire.com/1-wire-alternator-charge-indicator-light/
The only problem I had was the belt width in old Healeys is much wider that gm cars ‘agricultural size’ but my local alternator repair shop had the correct pulley.
I get what some of these guys are saying about originality but this particular mod can be easily reversed and it really improves the reliablility of the car.

Michael Oritt Avatar
LUSBY, MD, USA   USA
Thomas--

It's an interesting idea having the charging light function as a low-voltage meter but it's not giving you very useful information: 11 VDC is way too low a threshold as by the time system voltage has dropped that far you have a very dead battery that will definitely not start your car and you probably have a dead cell.

Here's a chart relating system voltage to the state of the battery's charge:

State of Charge Voltage
100% 12.7 - 13.2
75% 12.4
50% 12.2
25% 12.0
Discharged 0 - 11.9

The rule of thumb is that a 12 volt battery should read at least 12.8 and while running at anything over idle an alternator is going to cause a voltmeter to read 13.2 or more



Best--Michael Oritt
1954 Austin-Healey 100 (street)
1958 Elva Courier (track) FOR SALE
1959 Elva MK IV sports racer (track)
1961 Ginetta G4 (track)



Edited 1 time(s). Last edit at 2018-03-28 02:56 PM by Michael Oritt.

Luegolover Avatar
Luegolover Steve L
London, London, UK   GBR
Hello again,

Thank you for the useful information. I have a couple more thoughts that I would like clarification on if possible?

The C45 Alternator fits the bill perfectly, it is an alternator, it is cost effective and it is available in either +ve or -ve earth so I am still stuck with the same decision. I am not so stressed about the lights, I live in London and the chances of me having the car out in the dark anywhere other than a well lit road is pretty minimal so I will be able to cope with the original bulbs.

However, I would need some discreetly mounted USB charger sockets and whilst I can't imagine me having a radio at the moment it is possible that this would change. So:

1) Can I fit a USB socket under the dash that will charge an iPhone on a +ve earth car?
2) What are radio options for a +ve earth car

Finally, I want to run knew leads from the battery to the solenoid etc and need to know:

3) Are both the +ve and -ve terminals on a modern battery the same size?
4) What Amp rating should I go for?

Thanks in advance

MarkBD Avatar
MarkBD Mark D
LLandassillio, West Wales, UK   GBR
Hi,

Any modern device will need to be isolated from the chassis, unless you buy a period radio otherwise it will need to be isolated. The battery connectors are different sizes on modem batteries. I use a 55 Amp cable with my alternator rated at 45 Amp.
I think for the small amount of time and work involved you are better off converting to negative earth, and the detailing under the bonnet gives the appearance of originality.

Mark (100/4)

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