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Old 01-15-2019, 02:36 PM   #1
str8axle63
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Default Wiring for a 6 volt

I’m starting to re-wire my ‘42 ford truck. I normally use 16 gauge wire on my 12 volt trucks. Is it ok to use 16 on a 6 volt system?
Thanks[QUOTE]
Starting with tail lights
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Old 01-15-2019, 03:17 PM   #2
flatheadmurre
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Default Re: Wiring for a 6 volt

A 16 gauge can handle 10+ A...rear lights are 2 A brakelight are 7A and not for a long period...so should be plenty of headroom.

Last edited by flatheadmurre; 01-16-2019 at 02:39 AM. Reason: spelling...
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Old 01-15-2019, 05:42 PM   #3
Hyvolt
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Default Re: Wiring for a 6 volt

It's not the current, it's the voltage drop. At 6 volt, you need larger wire to maintain the brightest light possible. If you want to use incandescent bulbs id go at least 14.

Larger wire= less resistance=brighter bulbs.

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Old 01-15-2019, 07:36 PM   #4
rotorwrench
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Default Re: Wiring for a 6 volt

Different circuits need different gauges. 6-volt is low on the spectrum so in order to get amps through at that voltage you would need a minimum of 16 AWG. High amp lighting would need anything from 12 to 14. The longer a wire run is the higher the resistance so the next size gauge is used on long runs but on cars the runs aren't all that long. The tail lamps are about the longest run and the bulbs aren't high amp. High & low beam head lamps are about the highest amp load circuit in the average car. The horn is high but it is only intermittent. The generator charging circuit to the bus is about as high as it gets with exception to the starter motor. The starter should have a 0 to 2 gauge cable and larger if the battery is in the trunk.

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Old 01-15-2019, 08:08 PM   #5
JSeery
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Default Re: Wiring for a 6 volt

If you're interested in some original Ford wiring gauge on a 6v system here is a figure from a shop manual.
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Old 01-15-2019, 09:46 PM   #6
str8axle63
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Default Re: Wiring for a 6 volt

Thanks for your help, I’m starting with the tail lights, which obviously will be the longest wires, from your replies I should be good with 12 gauge, correct?
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Old 01-15-2019, 09:52 PM   #7
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Default Re: Wiring for a 6 volt

Use JSeery's diagram as your guide - the gauges are shown for the lighting circuits. Mostly 14 and 16 gauge. 12 gauge would be more than sufficient.
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Old 01-15-2019, 11:34 PM   #8
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Default Re: Wiring for a 6 volt

Quote:
Originally Posted by str8axle63 View Post
Thanks for your help, I’m starting with the tail lights, which obviously will be the longest wires, from your replies I should be good with 12 gauge, correct?
How did we get from 16ga to 12ga?
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Old 01-15-2019, 11:47 PM   #9
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Default Re: Wiring for a 6 volt

As per rotor wrench said the longer the distance the more resistance so I figured 12 would be best to cover the 9 ft distance
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Old 01-16-2019, 12:49 AM   #10
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Default Re: Wiring for a 6 volt

In summary, the capacity of a given wire in a circuit is dependent on its gauge and length. Google 6 volt wire charts and you'll find charts (gauge vs length) to download. I have some in my computer but this forum's program will not allow attaching them due to their file size or type.
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Old 01-16-2019, 02:23 AM   #11
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Default Re: Wiring for a 6 volt

Itīs all about how much current and how long the wire is (resistance).
A bulbs need the same amount of energy to be as bright as we want it to be...energy (watts) comes from volts x amps so when going to 12v we need half the current to get the same energy.
Needing to push half the current through the wires letīs us use thinner wires on 12v.
So why is the voltage drop such a big problen on 6v....if a wire has 0.1 ohm resistance and we push 10 amps through it we loose 1v in the wire...17% of the voltage is lost.
For the same amount of energy on 12v we have to push 5 amps through and loosing only 0.5v...thatīs just 4 % big difference.
The lenght of the wire in a vehicle is short (compared to wiring a house) so just calculate what current you are pushing through the wires and use the std charts for wires available.
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Old 01-16-2019, 02:39 AM   #12
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Default Re: Wiring for a 6 volt

The difference in voltage drop between a 16 and 14 GA cable using lets say 20ft for rear lights is just 0.03 ohm x 2A so you gain 0.03v.
For brakelights it will be a bit bigger 0.03 x 7A so you get 0.21V thatīs 3.5% less voltage drop...still the connectors and grounding is likely to be a bigger loss.
Probably more to gain by doing all connections well then oversizing the wires...
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Old 01-16-2019, 08:54 AM   #13
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Default Re: Wiring for a 6 volt

Good information for custom wiring, but if you are staying near original on the electrical you can just go with what the Ford engineers designed. When Ford went to 12v system the tail wiring was changed to 18ga. When you are custom wiring a vehicle you can increase the wiring size even if it is not really needed, however manufactures are not going to install a larger gauge size than is required.
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Old 01-16-2019, 09:02 AM   #14
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Default Re: Wiring for a 6 volt

I wouldn't use 16 gauge anywhere on a 6 volt car. The cost savings don't justify it.

As an example of voltage drop, I was having overdrive problems particularly at night that troubled me for a couple years. I eventually found that had rewired my overdrive power supply (from the ignition coil to the OD relay--- about 3.5 feet) and used 14 gauge. The 14 wire caused enough voltage drop to prevent my solenoid from engaging.
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Old 01-16-2019, 10:25 AM   #15
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Default Re: Wiring for a 6 volt

I agree with JSeery. If you're staying with 6 volt system stay with stock wire gauges Ford installed. If you convert any lights to LED I believe the current load is reduced.

An exception to stock wire sizes might be optional accessories such as a heater motor etc (I understand heater was still optional my year) if connected to the ignition switch. Then if you are adding electric wipers, electric fuel pump, etc you need to account for those "unplanned" loads. Previous owners of my car added so many accessories on my ignition circuit that the feeder wire to it overheated and roasted the wire insulation; as well it could overload the ignition switch itself. To solve that particular problem I put my accessories on a relay controlled circuit operated by the ignition switch.

As you probably know, horns and overdrive units are usually put on a separate fused circuit from the battery, and operated by a relay.

Last edited by Drbrown; 01-16-2019 at 10:32 AM.
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Old 01-16-2019, 10:46 AM   #16
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Default Re: Wiring for a 6 volt

Quote:
Originally Posted by str8axle63 View Post
Thanks for your help, I’m starting with the tail lights, which obviously will be the longest wires, from your replies I should be good with 12 gauge, correct?
Depends on the bulbs. LEDs would be the ticket and you could run those on 14-16 easily. As said before, every circuit has different requirements depending on amps drawn.
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Old 01-16-2019, 10:59 AM   #17
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Default Re: Wiring for a 6 volt

Not wanting to start a fight here...but 3.5ft of wire is in the milliohm range...itīs much more likely that you did a better job wiring it in then the person before and thatīs why it worked afterwards...the cable usually shows temperature rise before you loose a lot of voltage when things are real bad...the lost energy has to go somewhere...becomes heat.
1000ft of 14GA is about 3 ohm of resistance.
Pushing 10A through 3.5ft of 14GA you loose about 0.1v in the wire...
Often the connections and grounding to body/frame is a much bigger issue then the wire itself.
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Old 01-16-2019, 11:11 AM   #18
rotorwrench
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Default Re: Wiring for a 6 volt

16 gauge would likely be fine on truck tail lights unless a person was installing a trailer light plug or something of that nature. Add clearance lights and you would need a larger gauge. It's OK to use 14 if you want but larger is overkill. Another thing to think about is whether you are going to change from circuit breakers to fuses or the like. Both are to protect the wire and each gauge has a minimum size fuse or circuit breaker to protect it. You can use smaller amp fuses but never go over the amperage rating that any given wire size is rated for.

Ford used the old automatic reset type circuit breakers for the bus and a few glass tube type fuses to protect smaller light circuits like the dome light and the radio. Some were in line fuses and others are bus mounted but it depends on the year of manufacture as to how Ford designed them. Mac VanPelt's site has diagrams for cars but I'm not sure about trucks.
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Old 01-16-2019, 08:50 PM   #19
str8axle63
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Default Re: Wiring for a 6 volt

Quote:
Originally Posted by Drbrown View Post
In summary, the capacity of a given wire in a circuit is dependent on its gauge and length. Google 6 volt wire charts and you'll find charts (gauge vs length) to download. I have some in my computer but this forum's program will not allow attaching them due to their file size or type.
Thanks I googled it and it gave me a full chart of all the lights etc. that I need
Very helpful, thank you
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Old 01-16-2019, 08:51 PM   #20
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Default Re: Wiring for a 6 volt

Thanks for all your replies, I’m good now
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