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Old 08-01-2018, 02:35 AM   #1
Phil Gillespie
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Default 6v Battery negative ground

Just took delivery of a 46 Merury Coupe still on 6v. According to wiring diagram the positve is to earth.
However had a starting problem and hooked up a jump starter as per positive to earth and almost a melt dowm. This car is negative to earth?
Could this have been an error wehn perhap fitting the battery?
What is the effect of negative to earth.Generator appears to be chrging battery.
Is it just to refit the battery with positive to earth and negative to start solenoid and all should be ok?
Thanks,
Phil NZ
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Old 08-01-2018, 03:19 AM   #2
flatheadmurre
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Default Re: 6v Battery negative ground

You can hook up the battery either way and polarize the generator to charge it.
If you have an amp meter in the car it should read the wrong way with negative ground...so while charging it should read disharge.
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Old 08-01-2018, 03:41 AM   #3
Phil Gillespie
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Default Re: 6v Battery negative ground

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Originally Posted by flatheadmurre View Post
You can hook up the battery either way and polarize the generator to charge it.
If you have an amp meter in the car it should read the wrong way with negative ground...so while charging it should read disharge.

Hooked up this way with negative ground the amp meter is registering a positve charge. So to just leave it this way? or if change to re-polarise generator?
Phil NZ
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Old 08-01-2018, 05:55 AM   #4
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Default Re: 6v Battery negative ground

Phil, By all means you can leave it that way, BUT, all your other cars are probably 6 volt pos earth. Sooner or later, you'll get caught out with this one....easier in the long run to keep all your Fords wired as they should be [pos earth].
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Old 08-01-2018, 06:55 AM   #5
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Default Re: 6v Battery negative ground

If it is showing charge now...switching to pos earth means you have to change the direction the wire through the amp meter is going...usually just taking the ring connector off bending it to U-shape so it can be pulled out through the loop on the amp meter and sticking it back in from the opposite side of the loop.
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Old 08-01-2018, 07:04 AM   #6
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Default Re: 6v Battery negative ground

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I guess there are reasons to switch to negative ground but if I just acquired a car I was not familiar with my first inclination would be, is the battery in correctly.
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Old 08-01-2018, 08:38 AM   #7
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Default Re: 6v Battery negative ground

Sounds like someone has switched it over to negative ground. You can switch it back, but not sure it would be worth the effort, if it is working ok now I would leave it. If it has a "can" coil check and see how it is wired. Negative ground should have the (-) or Dist post connected to the distributor. If not that needs to be corrected.
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Old 08-01-2018, 03:13 PM   #8
Phil Gillespie
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Default Re: 6v Battery negative ground

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Originally Posted by JSeery View Post
Sounds like someone has switched it over to negative ground. You can switch it back, but not sure it would be worth the effort, if it is working ok now I would leave it. If it has a "can" coil check and see how it is wired. Negative ground should have the (-) or Dist post connected to the distributor. If not that needs to be corrected.

Thanks for that info. Will check that coil and i correct will leave as is and put a reminder sticker label at battery. As a reminder.
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Old 08-01-2018, 04:20 PM   #9
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Default Re: 6v Battery negative ground

They used positive to earth for max electron flow in the direction it flows best. Henry changed over in the model T days to pos earth. The difference isn't a lot but 6-volt batteries need all the help they can get sometimes.

Most stuff in the old cars isn't all that polarity sensitive that it can't be changed. On later cars with solid state electronics, polarity can NOT be changed. It would fry some electronics. The old 6-volt radios will work either way as long as it still has an old vibrator for voltage step up. If it gets changed to a later solid state vibrator then reverse polarity will kill it.
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Old 08-01-2018, 09:45 PM   #10
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Default Re: 6v Battery negative ground

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Originally Posted by JSeery View Post
Sounds like someone has switched it over to negative ground. You can switch it back, but not sure it would be worth the effort, if it is working ok now I would leave it. If it has a "can" coil check and see how it is wired. Negative ground should have the (-) or Dist post connected to the distributor. If not that needs to be corrected.

Checked at the coil and -ve is connected to distributor.
Removed all cables from battery to solenoid to starter motor. Cleaned up,
Cleaned off paint at firewall where earth secures.
It now spins over good on the fully charged 6v system with the -ve to earth so will leave it in this way..
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Old 08-01-2018, 11:11 PM   #11
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Default Re: 6v Battery negative ground

Not sure what -ve is, but if the coil is connected reverse polarity it will only function at about 80%.
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Old 08-02-2018, 12:23 AM   #12
Phil Gillespie
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Default Re: 6v Battery negative ground

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Not sure what -ve is, but if the coil is connected reverse polarity it will only function at about 80%.
\


-ve is my short cut for negative.
The negative terminal on coil is going to distrubutor as you had advised.
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Old 08-02-2018, 07:39 AM   #13
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Default Re: 6v Battery negative ground

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Originally Posted by Phil Gillespie View Post
\


-ve is my short cut for negative.
The negative terminal on coil is going to distrubutor as you had advised.
Phil NZ
Cool, then sounds like your all set! And I understand you shorthand now, I was just thinking I had never seen that marked on a coil.
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Old 08-03-2018, 07:17 AM   #14
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Default Re: 6v Battery negative ground

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Originally Posted by rotorwrench View Post
They used positive to earth for max electron flow in the direction it flows best. Henry changed over in the model T days to pos earth. The difference isn't a lot but 6-volt batteries need all the help they can get sometimes.

Most stuff in the old cars isn't all that polarity sensitive that it can't be changed. On later cars with solid state electronics, polarity can NOT be changed. It would fry some electronics. The old 6-volt radios will work either way as long as it still has an old vibrator for voltage step up. If it gets changed to a later solid state vibrator then reverse polarity will kill it.
Electrons only flow one way in a DC circuit. I do not believe there is any difference in performance as to which way current flows through the starter or any other device except the coil, which is polarity sensitive.
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Old 08-03-2018, 10:27 AM   #15
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Default Re: 6v Battery negative ground

Flow of electrons are the same...it´s about what becomes the sacrificial part in the system.
In positive earth you loose a few grams of iron from the body...in negative earth it eats up your copper connectors bolted to the ground.
In the battle between Ford(positive earth) and GM(negative earth) it might have been so that the big dragon won...
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Old 08-03-2018, 04:22 PM   #16
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Default Re: 6v Battery negative ground

Flow is always from negative to positive. The flow through a conductor wire is predictable and can be manipulated by keeping it close the power source and sizing the wire for the least resistance. The ground path is less predictable about its resistance to the flow and the pathway is not as easy to manipulate.

Electric starters are what made the change with Ford. The flow is better from a source (the battery negative post) to the starter via a known resistance conductor cable with a know length of run. The bottom line is that the starter worked better with the positive ground arrangement than it did with a switched polarity. The rest of the system could care less.

When 12-volt came along, resistance of the conductor cable wasn't so much of a factor with twice the voltage to kick it through. When alternators came along, the diode life is a bit more reliable with negative ground so that sort of sealed the deal.
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Old 03-04-2020, 08:23 AM   #17
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Default Re: 6v Battery negative ground

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Originally Posted by rotorwrench View Post
Flow is always from negative to positive. The flow through a conductor wire is predictable and can be manipulated by keeping it close the power source and sizing the wire for the least resistance. The ground path is less predictable about its resistance to the flow and the pathway is not as easy to manipulate.

Electric starters are what made the change with Ford. The flow is better from a source (the battery negative post) to the starter via a known resistance conductor cable with a know length of run. The bottom line is that the starter worked better with the positive ground arrangement than it did with a switched polarity. The rest of the system could care less.

When 12-volt came along, resistance of the conductor cable wasn't so much of a factor with twice the voltage to kick it through. When alternators came along, the diode life is a bit more reliable with negative ground so that sort of sealed the deal.
Finally a Clear and correct explanation. Thank you!
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Old 03-04-2020, 12:04 PM   #18
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Default Re: 6v Battery negative ground

I agree. Good, clear explanation. Rotorwrench, sounds like you have a background as a teacher/instructor.

Now that we've gotten into the weeds of electron flow, this student has a follow-up question: wouldn't the unpredictable resistance in the ground part of the circuit have the same effect on current flow thru the circuit, before or after the starter?

Last edited by JayChicago; 03-04-2020 at 12:31 PM. Reason: remove a typo
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Old 03-04-2020, 12:57 PM   #19
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Default Re: 6v Battery negative ground

Positive or negative has nothing to do with how easy current flows...it´s a closed loop that goes from battery and back to it again...sum of all resistance on feed or ground side ads up.
If it would be more efficient todays cars in the hunt for that last % of economy would be pos ground....think of all motors not only starters used in a modern car.
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Old 07-29-2021, 12:09 PM   #20
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Default Re: 6v Battery negative ground

I appreciate the clear explanation
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