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Old 11-03-2008, 02:00 AM
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Help...6volt to 12volt conversion issues

Hey Folks...

Me again...I seem to be posting lots of questions, but I have never worked on anything pre-60's..

ANyhoo, I will be converting my 41 Plymouth from 6 volts to 12 volts when I change the engine and trans. I was wondering if...

1. Can I used the existing wiring harness in the car when I go to 12 volts?
2. Will the switches take the addition juice?
3. Will the headlights, brake lights, etc. work or will they pop?
4. Will the car still be positive ground (as it is now)?

Thanks!

Ty
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Old 11-03-2008, 02:59 AM
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Almost everything that uses electricity, the loads, will have to be changed, lights, wiper motor, radio, gauges. Possible exception, the starter may be OK. The coil probably not.
The actual wiring, and switches will like the change. Generally the current through everything will be less.
The lights will pop if you do not change them.
If the starter turns the correct way with a negative ground, you could probably convert the car to negative ground to match any electrical components you get in the future.
Will the car have a generator, or an alternator? Generators are easy to switch to negative ground, alternators, not so much.
I am not lucky enough to own this car, so I do not know all the minor details of everything, hopefully someone else does.
I have an old tractor that I converted from 6 volts, positive ground to 12 negative ground. No lights, just a starter, and a ignition coil. I just put an extra ballast resistor in the circuit for the coil. For the starter, I just ran 12 volts to it.
The starter on the tractor is wired inside so it only turns one way, positive ground, or negative ground. A starter motor on any car is an "overloaded" electric motor, by that I mean they can only run for about 30 seconds, or so, and you have to let them cool down.
An electric motor is a weird animal. An electric motor "feels" the load on itself, and if there is no load, it runs faster, and the faster an electric motor spins, the less current it uses. When you run a 6 volt electric motor on 12 volts, it will spin faster, and the current going through it will not double with the doubled voltage. Quite often, on a car starter, the faster turning starter will turn the motor over faster, and the car will start much faster, and you will actually spend a lot less time cranking the engine with a 6 volt starter running 12 volts, than running 6 volts on a 6 volt starter. Your starter may be different, and not live as long with 12 volts. Keeping the car tuned so it starts easy will make your starter last longer on any car.
Lights are not like that. Lets say you have a six watt light, in a taillight. you have six volts going to that light. That light will use one amp of current.
volts times amps equals watts. E*I=W
That lamp will also have six ohms of resistance.
If you run 12 volts to that same lamp, that light will try to use 2 amps of current. Twice the voltage, twice the current into the same resistance.
You now have 2 amps times 12 volts going into that lamp. That 6 watt lamp is now using 24 watts. The lamp will burn very bright, but will burn out in a very short time. In my example, you get a taillight lamp with 24 ohms of resistance, instead of 6 ohms you had before. With 12 volts, that lamp now flows only a half of an amp. 1/2 amp times 12 volts gives you a six watt lamp.
Of course, when you buy new lamps for your lights, you do not ask for a lamp by resistance, you get lamps by the voltage, and the watts.
I hope this is not too confusing. I am no Docvette.

Last edited by DanielC; 11-03-2008 at 03:17 AM.
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Old 11-03-2008, 03:17 AM
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Hey DanielC...Wow! That's a lot of info...I will actually be swapping in a modern (ie. 1960's) V8, so the starter won't be an issue as I'll be using a new one. Same goes for the alternator...the original generator is coming out with the flathead 6. Wipers are vaccuum, radio is non existent, coil will be new.

I will change the light bulbs. Thanks!

Ty
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Old 11-03-2008, 03:38 AM
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DanielC provided a lot of good information for you...let me add my 2 cents. Take a close look at the condition of the original wiring. The original wiring was fabric covered, rubber insulated wire. After 60+ years, it has a tendency to deteriorate. You may find that at least some of your wiring should be replaced. It's worth a close look, and might save you a lot of grief later on.
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Old 11-03-2008, 04:33 AM
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Oldguy48, you are right. Check the condition of the wires. Between time and the possibility of some rodents chewing on something, that could cause some grief. Any connectors, in the harness could also be corroded, or bad.
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Old 11-13-2008, 05:13 PM
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You didnt say what running gear you will be using? Preferable Chevy! That is about the easiest wiring to do ground up on any oldie. Schematics and diagrams for basic applications are really old school and easily obtained. I've done three old jeeps in GM without any issues ever! Start by ripping out all the old stuff and plan on using all new everything. U-pull it yards can save you a lot in materials and parts. Bring it over and I'll help you in GM.
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Old 11-14-2008, 05:55 AM
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If you're pulling the old drive train, obviously you're starting with a 'clean slate'. I WOULD recommend changing the wiring too, your light bulbs are obvious. Consider other things like.....heater motor's etc.

Good Luck
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Old 11-14-2008, 08:16 AM
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You do not need to change the wires. If the wires are in good shape, like the insulator is not dry or brittle then use it. You are using half the current for the same given power. Volt X current= power. The only thing I would check is heater motor in the car. It may spin backward if it pos ground and burning it out. The bulbs have to change to 12V. The switches will handle the power with no problem.

Last edited by lg1969; 11-14-2008 at 08:22 AM.
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