12 VDC Wiring

JohnB15632

JohnB15632

Well-known member
What changes are required to the attached drawing for using a 12 VDC Negative ground vs the 6 VDC positive ground?

Does a similar drawing exist for the 12 VDC Neg Ground?

thanks,
 

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Swap the wires to negative on the coil , ammeter and the battery . This will work if you install a twelve volt battery connected with negative ground . I run some of my model A's on twelve volt positive ground with all new original style wiring harnesses from Brattons and no changes to the wiring is needed .
 
Purdy Swoft said:
Swap the wires to negative on the coil , ammeter and the battery . This will work if you install a twelve volt battery connected with negative ground . I run some of my model A's on twelve volt positive ground with all new original style wiring harnesses from Brattons and no changes to the wiring is needed .
Click to expand...

Wouldn't you need to change the coil and globes to 12 v versions and drop 12 volts to 6 for the horn? The horn will work on 12 volts but it sounds more like a scream, or was that my wife?
 
Usually a one point five OHM coil is used with six volts . A one point five OHM coil can be used on twelve volts if a ballast resister is used . I use a three OHM coil on my twelve volt converted model A's . A three OHM coil will run on twelve volts without the need of a resister for a cleaner more original look . To save typing . I figure that it should be mostly common sense that twelve volt bulbs would be necessary for twelve volt use . A resistor will be needed for a six volt horn that is used on twelve volts , same for six volt windshield wiper motors or any other six volt accessories that are used on twelve volts . Besides the replacement of the bulbs , the six volt battery will need to be changed to a twelve volt battery . I figure that most would know this but I will add the battery for those that wouldn't . John B asked what wiring changes to the wiring drawing would be needed . I listed the wiring changes to run twelve volts If fnegative ground . No wiring changes are needed to run twelve volt positive ground . No harm meant . I figure that anybody that didn't know that the bulbs would need to be changed to twelve volts when making a twelve volt conversion would probably never be able to make a twelve volt conversion , no matter what .
 
Purdy Swoft covered most of the things that need to be changed to run on 12 Volts positive or negative ground. Would recommend that you change the Bendix on the starter to the newer type as the 6V starter motor really spins on 12 Volts. If you would like a list of the bulbs for 12V or 6V and other electrical info send me an email and will send it to you. My email is jrelliott42@gmail.com
 
Thanks jr . I did use the modern starter drive and forgot to mention it . The modern starter drive wouldn't be a bad idea even with six volts ..
 
What changes need to be done to the starter if converting to negative ground ? Seems like the starter will rotate in the wrong direction if not modified. Would the field contacts just need to be reversed ?
 
Mulletwagon said:
What changes need to be done to the starter if converting to negative ground ? Seems like the starter will rotate in the wrong direction if not modified. Would the field contacts just need to be reversed ?
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Purdy is right about the coil and I have no problem with anything else he said.
The starter will still turn in the same direction so there is no need to fiddle in there unless you want to change the field windings to all in series for 12 volts. Many people leave the starter unaltered although I switch the windings around jus to make life easier on the bendix.
 
Mulletwagon said:
What changes need to be done to the starter if converting to negative ground ? Seems like the starter will rotate in the wrong direction if not modified. Would the field contacts just need to be reversed ?
Click to expand...

Converting to negative ground will not require any modifications to the starter . Ground has no effect on direction of rotation . Some change the field coils . I do use the modern starter drive but have had no problems with the original setup .
 
I use a Pertronix flame thrower coil on my twelve volt converted roadster . I use the three OHM version that needs no resister.
 
Purdy Swoft said:
Thanks jr . I did use the modern starter drive and forgot to mention it . The modern starter drive wouldn't be a bad idea even with six volts ..
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Hey Purdy, which modern starter drive do you run/suggest? I'm running 12V on an original 6V starter and my bendix jingles a bit occasionally :rolleyes:.
 
Here's a 12 volt neg ground schematic off the net. Some discussion in other threads about pros/cons about relocating the condenser to the firewall. Make sure you have a polarity check for the coil terminal wires. I install the coils with the terminals up.
 

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Bratton offers a made in the USA modern starter drive , part number 15961 price $36.95 , Snyders also offers the modern starter drive on page A-154 . This part can probably be purchased locally if you know what modern car it was used on .
 
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