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Old 07-23-2016, 02:20 PM   #1
dbrist
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Default 12v wiring diagram

I've been searching these threads for a while and I might have missed it, but I was wondering if anyone had a 12v negative ground wiring diagram
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Old 07-23-2016, 03:02 PM   #2
Gary WA
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Default Re: 12v wiring diagram

No but in the Model A For Mechanics Handbook Vol. 2 shows it all.
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Old 07-23-2016, 03:05 PM   #3
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Default Re: 12v wiring diagram

Thanks ordered it a month ago and still waiting
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Old 07-23-2016, 03:09 PM   #4
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Default Re: 12v wiring diagram

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Originally Posted by dbrist View Post
Thanks ordered it a month ago and still waiting
also How to restore your Model A. Vol 8 has info too.
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Old 07-23-2016, 05:22 PM   #5
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Default Re: 12v wiring diagram

Only difference between 6V positive ground schematic and 12V negative ground schematic is the polarity of the battery. Just have to repolarize the generator after changing the battery connections if you are going to use the same generator. Make sure you have negative ground alternator if using an alternator. The electrons do not care which way they travel. They just move from negative to positive.
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Old 07-23-2016, 06:08 PM   #6
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Default Re: 12v wiring diagram

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Trucks already 12v system just like schematics to trouble shoot with
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Old 07-23-2016, 06:54 PM   #7
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Default Re: 12v wiring diagram

Use this just switch the battery polarity around on the schematic
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Old 07-23-2016, 10:50 PM   #8
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Default Re: 12v wiring diagram

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Originally Posted by dbrist View Post
I've been searching these threads for a while and I might have missed it, but I was wondering if anyone had a 12v negative ground wiring diagram
One only has to swap the wires on the ammeter and the coil to change the polarity.

To increase the voltage:

The coil needs to be changed or a ballast resistor added.
The horn needs a resistor or needs to be rewound.
Here is where we can get into a debate, one camp says leave the starter alone and the other says to have it converted to 12 volts. Take your pick.
Of course the bulbs have to be replaced.
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Old 10-03-2017, 09:55 PM   #9
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Default Re: 12v wiring diagram

im new..pls tell me the correct wiring for a 12V model A..what wires go where on coil?
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Old 10-04-2017, 12:20 AM   #10
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Default Re: 12v wiring diagram

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im new..pls tell me the correct wiring for a 12V model A..what wires go where on coil?
12v negative ground, battery positive to + side of coil, - side of coil to points (via switch). See Mike's post #8 above.

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Old 10-04-2017, 05:28 AM   #11
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Default Re: 12v wiring diagram

Points are wired same as the battery. Whichever wire goes to ground from the battery goes to the points from the coil.
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Old 10-04-2017, 01:37 PM   #12
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Default Re: 12v wiring diagram

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im new..pls tell me the correct wiring for a 12V model A..what wires go where on coil?

The point to point wiring makes no difference what the voltage the battery is.
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Old 10-09-2017, 09:32 PM   #13
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Default Re: 12v wiring diagram

This is a complete discussion on converting to 12v as well as adding turn signals.

http://cedarcreekas.org/TechTopics/1...rn_Signals.pdf
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Old 06-24-2020, 08:25 PM   #14
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Default Re: 12v wiring diagram

I just made a 12v Negative Ground diagram after rewiring mine. This is a tried and tested diagram. Here is how you wire the ignition system. This diagram does not include lighting and horn.

NOTE: The Aftermarket "pop-out" style ignition cable connects to the "ON" position of the key switch. The "OFF" Position of the key switch connects to the NEG side of the coil. The key switch simply completes that circuit. DO NOT supply the "pop out" cable with 12v+!! Also in this diagram, you are looking at the BACK of the Ammeter where the studs are located. This diagram shows a GM 10Si one wire alternator, which self excites. Make sure you have a alternator that excites at LOW Rpm or it will not charge at idle. If you run a 3-wire alternator, DO NOT supply 12v constant to the exciter while the car is off. It WILL burn up!
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Old 06-24-2020, 09:26 PM   #15
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Default Re: 12v wiring diagram

30AModel,

You need to check your diagram as the ammeter is not connected and the alternator connects directly to the battery.

Marc
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Old 06-24-2020, 09:43 PM   #16
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Default Re: 12v wiring diagram

The ammeter is connected to the distribution block and the main alternator lead connects to the Positive post on the starter, which in turn feeds back to the battery.
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Old 06-25-2020, 09:51 AM   #17
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Default Re: 12v wiring diagram

Ammeter originally was wired to show only battery current in/out. 30AModel moved it to the load side; it shows only "charge" of the entire load (minus coil) from alternator and/or battery. (I suggest moving coil to other side of block so its current will register also.)
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Old 06-25-2020, 10:19 AM   #18
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Default Re: 12v wiring diagram

Quote:
Originally Posted by Mitch//pa View Post
Use this just switch the battery polarity around on the schematic
And the coil.
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Old 06-25-2020, 01:33 PM   #19
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Default Re: 12v wiring diagram

Don't forget to reverse the wires at the ammeter when changing polarity or the ammeter will read backwards .
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Old 06-26-2020, 01:44 PM   #20
Chuck Sea/Tac
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Default Re: 12v wiring diagram

Am I wrong?? The ampmeter has to have current flowing through it, or else how would it register current? If one side isn’t connected to anything, I fail to see how it would measure the current.
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Old 06-26-2020, 03:38 PM   #21
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Default Re: 12v wiring diagram

My apologies to all. I did indeed forget to finalize the Ammeter wiring on the diagram. I threw this diagram together shortly after rewiring my car. The ammeter (on mine) pulls power from the distribution block, and all accessory power comes off the other side of the Ammeter. I opted to connect the coil directly to the distribution block, vs the ammeter. I am sorry for the confusion on that. I will update my diagram and repost it soon.
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Old 06-26-2020, 03:58 PM   #22
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Default Re: 12v wiring diagram

My apologies to all. I did indeed forget to finalize the Ammeter wiring on the diagram. I threw this diagram together shortly after rewiring my car. The ammeter (on mine) pulls power from the distribution block, and all accessory power comes off the other side of the Ammeter. I opted to connect the coil directly to the distribution block, vs the ammeter. I am sorry for the confusion on that. I will update my diagram and repost it soon.
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Old 06-26-2020, 04:55 PM   #23
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Default Re: 12v wiring diagram

I run my 1931 roadster on 12 volt positive ground and no wires needed to be changed . I installed a three OHM coil in place of the original type one point five OHM coil . An original type one point five OHM coil can be used if a ballast resistor is used at the coil connection . The resistor prevents the full 12 volts from entering and burning out the six volt coil in such cases . The larger gauge original size wiring , if in good condition can carry 12 volts better without overheating than smaller gauge wire that is often used on twelve volt applications . Some prefer negative ground for certain accessories . I don't use any accessories and run mine as original . The difference in my 12 volt model A is in the battery and coil . I use the large original cable and wire from the distributor to the ignition switch . I don't use the original pop out switch . I use a more modern ignition switch . I adjust the generator for a 10 amp maximum charge rate . I use the Fun Projects can style voltage regulator in place of the cut out. The Fun projects voltage regulator looks just like the original cut out but gives voltage regulation similar to modern vehicles . Every thing still looks and operates like original but is a more powerfull . I install 12 volt bulbs and use resistors on any 6 volt accessories that are used . I've run the unmodified original starter and generator on 12 volts for many years with no problems . Twelve volt batteries and parts are readily available . I get a more powerful system that still looks completely original .
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Old 06-26-2020, 05:08 PM   #24
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Default Re: 12v wiring diagram

I updated my wiring diagram and fixed the ammeter wiring. I realize there are many ways to "skin a cat" when it comes to rewiring for a 12v neg ground system. I am simply sharing this, as it works for me and should help others find their way when rewiring. As always, you do not have to follow this exact diagram. It simply gives you an idea of what works. You can add, remove, or change anything to your liking. Thank you all for correcting me and bringing my goof ups to my attention.
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Old 06-26-2020, 06:18 PM   #25
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As said , there are many ways to do this operation . I wasn't correcting or trying to say that your method was wrong . I was only sharing and explaining how I did mine .
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Old 06-26-2020, 07:05 PM   #26
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Purdy Swoft,

Absolutely. I was by no means upset by that at all! I hadn't even realized that I failed to complete that part of the diagram. I really am glad it was brought to my attention. Thanks for the input!
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Old 06-27-2020, 02:29 AM   #27
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Default Re: 12v wiring diagram

No wires change what so ever. Aren’t we verging on over thinking this?
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Old 06-27-2020, 08:52 AM   #28
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Default Re: 12v wiring diagram

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No wires change what so ever. Arenít we verging on over thinking this?
Yes, but a few wires do need to be changed if switching from positive ground to negative ground. Coil and ammeter wires are two.
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Old 06-27-2020, 09:00 AM   #29
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Default Re: 12v wiring diagram

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Old 06-27-2020, 09:28 AM   #30
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Default Re: 12v wiring diagram

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Originally Posted by Bill G View Post
No wires change what so ever. Aren’t we verging on over thinking this?

I run mine,12 volt positive ground and NO wires were changed , it has worked perfectly for years . If converting to negative ground wires will need to be changed .
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Old 06-27-2020, 01:59 PM   #31
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Default Re: 12v wiring diagram

In order to run negative ground the battery cables need to be connected as negative - to ground and +positive should connect to the starter switch . This will convert the system to negative ground ..The wires at the coil connection need to be switched and the wires at the ammeter need to be switched . If converting to 12 volt it will be necessary to use a resister at the coil connection or better still use a three OHM coil and no resister will be needed . I use the Pertronix flamethrower coil with great noticeable results . The Pertronix coil looks the same as most replacement coils but gives instant starts and gives extra power that can be felt in the seat of the pants .
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