When Re wiring Vehicle wire size

[Sactownog]

hey friends, I have re-wired a few vehicles in my time and I am planning on re-wiring my 33 Dodge starting this week. the wires are very beat up and the sheathing is crumbling off it and can cause issues so I plan to redo all wires and clean it up. 

 

my question: the vehicle is a POSITIVE GROUND 6V system. I have never worked on a Positive Ground system before and I have read that the wires tend to be thicker as to move power more efficiently. 

 

if there is anyone with experience on this I would like any tips, I do plan to replace the wires with the existing size so as to remove a wire and replace with same size that was used. I just did not know if there is something I should do to either upgrade the wires or just stick with standard size that is on the vehicle... 

 

one electrical problems I have that I know of is that my headlight switch that controls the HIGH BEAM/LOW BEAM lights may be connected wrong as

1 click with my foot and the headlights come on,

2nd click and only the driver light comes on

3rd click and only passenger light comes on

then click again and back to both headlights being on.

[keiser31]

I suggest getting a wiring harness from these folks....it will work out better for you in the long run....I got mine from them....http://www.riwire.com/

[Bhigdog]

22 minutes ago, keiser31 said:

I suggest getting a wiring harness from these folks....it will work out better for you in the long run....I got mine from them....http://www.riwire.com/

 

+2 on that suggestion...Excellent product, excellent instructions, excellent support......................Bob

[Guest]

Positive or negative has no impact on the wiring.  The electrons can run exactly the same either way. Only the generator, starter, gas gauge and radio need to be polarity correct.

Whatever is wired (home, business, motor home or automobile) always has bigger gauge wire at the source and smaller wires at the final appliance.  Look at the big wires coming in to your breaker panel at home and the small wires at you wall plugs.

I believe that your headlight dimmer is wired correctly.  Many car manufacturers in the 30's tried various and sundry ways to "dim" headlights.  High beam/Low beam was not the normal then.

For as little as you seem to know about automotive electricity you do need a manual with a wiring diagram and I think you need to purchase a ready made harness.  It will probably save you time, trouble and money in the end.

 

I have never rewired a car of mine (my daily driver is 87 years old (500,000 miles) and has had one wire spliced in where it was frayed).  I added one wire to be able to have turn signals.

I made a wiring harness for two of my friends and if I were asked again I would send them to http://www.riwire.com/.  By the time you buy the correct colour coded wire in the correct gauge, all the ends and connections, conduit and tape, etc., and pay for my time they are more economical.

 

IMHO too many people rewire cars that don't need to be rewired. 

Edited January 24, 2018 by Guest (see edit history)

[Frank DuVal]

3 hours ago, Tinindian said:

The electrons can run exactly the same either way.

 

I would have phrased it: The electrons just run in the opposite direction. This is the difference in positive vs negative ground DC systems. Of course they do the same work.

 

Tinindian is right, same awg wire for positive and negative ground, it is the fact it is a 6 volt system means the wire carries twice the current, so the wire is twice as large (crossection in circular mils) as the 12 volt wire for the same power device.

[joe_padavano]

30 minutes ago, Frank DuVal said:

 

I would have phrased it: The electrons just run in the opposite direction. This is the difference in positive vs negative ground DC systems. Of course they do the same work.

 

 

Well, in that case you would have phrased it incorrectly. On a DC circuit, electrons always flow from the negative battery terminal to positive. The electrons neither know nor care which battery terminal is connected to the metal structure. The sheet metal is simply being used to replace wires on one side of the circuit. It doesn't matter which one.

[Frank DuVal]

Exactly. In the negative ground car, the electrons flow from the chassis through the device being powered. In the positive ground car, the electrons flow through the devices to the chassis!

 

So, the electrons flow in the opposite direction in the devices, I should have phrased.

 

Or, The electrons flow in the opposite direction in the chassis.

[retiredmechanic74]

To get back to the original question, 14 gage wire will handle everything "from" the fuse box or the "secondary side" of the main accessory lead. Anything that is on the primary side should be 12 Gage and the battery cables "for the six volt system" should be 2 to 4 Gage 2 being better for voltage flow. 

[joe_padavano]

10 hours ago, Frank DuVal said:

Exactly. In the negative ground car, the electrons flow from the chassis through the device being powered. In the positive ground car, the electrons flow through the devices to the chassis!

 

So, the electrons flow in the opposite direction in the devices, I should have phrased.

 

Or, The electrons flow in the opposite direction in the chassis.

 

Sorry, but this is still not correct.  The electrons don't know if they flow in the chassis before the using device or after, nor do they care.  That's a timing issue, (before or after use) not a "direction" issue. If you replaced the chassis with another piece of copper wire, the circuits would be exactly the same and we wouldn't even be having this discussion. I realize you are being somewhat humorous, but promoting ideas like this is only contributing to the dumbing of America.  We're woefully uninformed as a public when it comes to technical issues; please don't contribute to that.

 

Lamp filaments aren't directional and don't care. Switches don't care. Starter motors don't care. You can jump start a positive ground vehicle from a negative ground vehicle.  You can use the same battery in both.  The "flow" of electrons does not change.

[Rusty_OToole]

The reason you need bigger wires is because 6 volts needs bigger wires than 12 volts. So the wires must be twice as big as a modern car.

 

Use the same size wires as the original. I mean the wire itself not the insulation. Get a factory wiring diagram if you can, the wire sizes will be marked on it. Don't make the mistake of wiring the whole car with one color of wire. This will make a nightmare for you and everyone who ever works on it. Best thing to do is buy a wiring harness. It will save you time and money and do a better job for you.

[Bhigdog]

If you wish to do your own rewiring you can buy the correct gauge/color code wire by the foot and terminals by the piece from Rhode Island Wiring..................Bob

[Restorer32]

Neutron walks into a bar. "Gimmee a beer". Bartender complies and the Neutron downs the beer. "How much" says the Neutron. Bartender says....wait for it..."For you, no charge".  Seriously, do yourself a favor and buy a pre made wiring harness. We have used Rhode Island Wiring for years with no complaints.

[joe_padavano]

48 minutes ago, Rusty_OToole said:

The reason you need bigger wires is because 6 volts needs bigger wires than 12 volts.

That's like saying "do it because I said so..."

 

The real reason is current, not voltage. Wire is sized by the amps that it has to carry, not the voltage (otherwise plug wires would be larger than battery cables). Voltage sizes insulation thickness, current sizes the copper.

 

Since watts = volts x amps, half the voltage requires twice the amps for the same load, and THAT'S why you need twice the copper area (not diameter).

[Spinneyhill]

Voltage is a potential. It is the driving force for the current.

 

So to get twice the conductor area, you need a conductor 1.414 (root 2) times the diameter.

 

@joe_padavano surely the electrons go the other way through the vehicle? - to chassis to driven item to switch to +. Or - to switch to driven item to chassis to +? So they either hop onto the chassis off the battery - or off the chassis onto the battery +?

[Restorer32]

Actually the electrons do not move. They just transfer their potential from one to the next much like the balls on a string toy that band into one another without moving.

[joe_padavano]

24 minutes ago, Spinneyhill said:

Voltage is a potential. It is the driving force for the current.

 

So to get twice the conductor area, you need a conductor 1.414 (root 2) times the diameter.

 

@joe_padavano surely the electrons go the other way through the vehicle? - to chassis to driven item to switch to +. Or - to switch to driven item to chassis to +? So they either hop onto the chassis off the battery - or off the chassis onto the battery +?

Still only moving from batt negative to batt positive.

[retiredmechanic74]

I don't understand all the jargon? Technically voltage has nothing to do with it, amperage is what should be the concern that's the main reason for the fuse and wire size. When I installed my Hydrogen Cell it demanded 30 amps to run, I took two 12 Gage wires of equal length and tied the wires together with one spade connector at each end to handle the 30 amps.      

[joe_padavano]

One last try, then I'm done.

 

First, a circuit for a headlight with only copper wires.  Second a circuit with negative ground.  Third a circuit with positive ground.  Someone show me how the electron flow is "reversed".

 

 

[Frank DuVal]

Again, Joe, just look at your two last pictures. You are proving my point!  

 

The electrons in the chassis are going in opposite directions through the chassis in the last two pictures. In the negative ground car, the electrons flow from the source (battery) trough the chassis to the loads (lights, etc.). In the positive ground car, the electrons flow through the wire to the loads first then through the chassis. If you hooked a DC ammeter on the cable going from the battery to chassis in each case, it will read opposite, indicating the flow of electrons is reversed!  

 

If one were to use a clamp on ammeter on the chassis to battery cable, for a positive reading, the arrow would be opposite in each case. Hence, reversed electron flow in that cable.

 

I never meant the electron flow in the battery was reversed, just in every other device. Not that lamps and series wound motors care.... 

 

And yes, Restorer is correct, the electrons act like pool balls touching in a line, so there appears to be flow, since I put one pool ball into the line, and a pool ball comes out the other end. Just not the same pool ball.

 

Next we shall loose everyone one and discuss positrons*, that flow in the direction of diode arrows,..... Ha!  We know that as conventional current flow. Or, Ben Franklin's error.

 

*yes, positrons are real, just not used in this way. It is a play on words for humor.

[37_Roadmaster_C]

     Ok guys, I am going to jump in here and call BS on the irrelivant argument about electron flow!  Joe is correct if you want to grade a test for an engineering position. The real point of this topic is wire size and I mean the size (cross sectional area) of the copper. It has been explained that the current (amperage) required to do a specific amount of work (light a lightbulb, for example) is doubled in a 6 volt system as compaired to a 12 volt system. The more amps required means the wire needs to be larger to allow the amps through with acceptable voltage loss. The techno jargon is not needed to explain this to a non tech person. If you want an explaination of the scientific reasons including the math to prove why a certain wire size is used, feel free to take an electrical engineering course from a respectful school!!!

 

   Sorry for the snarkey response, but it serves no purpose for the original poster, to argue scientific nitpicking points. I have lived and worked on both sides of this fence and the point is moot for practical answers.

 

Now one thing we seem to agree on is that buying a premade harness is generally more practical than making one yourself.  Just for info, I bought my replacement harness from YNZ in California. They are just another option to check out. The harness for my 37 Buick was custom ordered with some modifications to meet my wants. The harness is perfect and the documentation is great. The mods I ordered were a larger wire size for headlight circuits, a rework to allow turn signals with the existing lights and a couple of extra wires for driving lights, spotlight and a possible future electric fuel pump. The finished harness looks like Buick made it in 1937.

 

Again, sorry for the rant .

Edited January 26, 2018 by 37_Roadmaster_C
spelling (see edit history)

[Frank DuVal]

I apologize for running the thread off track. All it took was a simple comment on the direction of electron flow. 

 

Good to hear about YNZ for another source of harnesses.

 

[37_Roadmaster_C]

No problem Frank. I just get pissy about things like this because I have been in the middle before.  Now if you want a real productive argument, lets talk metric VS imperial pros and cons............  I'm running out now...  is afraid of fire....

[Restorer32]

Let's talk about how you can determine the weight of a car by measuring the contact area of the tires on the pavement and muliplying by the tire pressure. That always gets folks arguing.

[Ben Bruce aka First Born]

9 hours ago, 37_Roadmaster_C said:

     Ok guys, I am going to jump in here and call BS on the irrelivant argument about electron flow!  Joe is correct if you want to grade a test for an engineering position. The real point of this topic is wire size and I mean the size (cross sectional area) of the copper. It has been explained that the current (amperage) required to do a specific amount of work (light a lightbulb, for example) is doubled in a 6 volt system as compaired to a 12 volt system. The more amps required means the wire needs to be larger to allow the amps through with acceptable voltage loss. The techno jargon is not needed to explain this to a non tech person. If you want an explaination of the scientific reasons including the math to prove why a certain wire size is used, feel free to take an electrical engineering course from a respectful school!!!

 

   Sorry for the snarkey response, but it serves no purpose for the original poster, to argue scientific nitpicking points. I have lived and worked on both sides of this fence and the point is moot for practical answers.

 

 

 

Again, sorry for the rant .

 

 No apology needed!  You are right on.  

 

  Ben

[hchris]

14 hours ago, Ben Bruce aka First Born said:

 

 No apology needed!  You are right on.  

 

  Ben

 

Amen to that 

[Friartuck]

In a lot of the circuits, 14-12 Gauge wire would be appropriate. There is a possibility where some circuits come together the use of 10 gauge wire is needed. Example Battery/Generator to Ammeter. Also suggest consider adding in a connector concealed behind the dash for a battery tender. A good safety precaution is to include a battery master disconnect switch. Soldering lug terminals is best for good connections: http://www.secondchancegarage.com/public2/electrical-connections-1.cfm

 

[Larry Schramm]

On ‎1‎/‎25‎/‎2018 at 2:31 PM, retiredmechanic74 said:

I don't understand all the jargon? Technically voltage has nothing to do with it, amperage is what should be the concern that's the main reason for the fuse and wire size. When I installed my Hydrogen Cell it demanded 30 amps to run, I took two 12 Gage wires of equal length and tied the wires together with one spade connector at each end to handle the 30 amps.      

 

Amperage(current) and voltage has everything to do with it along with resistance in the circuit.  Ohm's law of V = I x R which is voltage = current x resistance in the circuit defines the electrical activity.  

 

For your second statement about using two parallel 12 gauge wires for a 30 amp circuit is down right scary.  The 12 gauge wires are only rated for 20 amps separately.  Putting them in parallel is bad wiring.  If one of the individual wire ends develops a poor connection you could be trying to put all 30 amps in a wire too small to carry the current. Usually at that point you will be letting the smoke out of the wire. Not safe. 

 

To design for that size of current flow you should have a single 10 gauge wire at least and maybe an 8 gauge.

[retiredmechanic74]

12 hours ago, Larry Schramm said:

 

Amperage(current) and voltage has everything to do with it along with resistance in the circuit.  Ohm's law of V = I x R which is voltage = current x resistance in the circuit defines the electrical activity.  

 

For your second statement about using two parallel 12 gauge wires for a 30 amp circuit is down right scary.  The 12 gauge wires are only rated for 20 amps separately.  Putting them in parallel is bad wiring.  If one of the individual wire ends develops a poor connection you could be trying to put all 30 amps in a wire too small to carry the current. Usually at that point you will be letting the smoke out of the wire. Not safe. 

 

To design for that size of current flow you should have a single 10 gauge wire at least and maybe an 8 gauge.

Just a heads up I studied OHM's Law and was only trying to give a simple answer to a simple question. And secondly the doubling of the 12 Gage wire is being controlled by a pulse-width modulator and has been in service for over 6 years now, exposed to the elements, and I failed to mention the solder joints, the 30 amp fuse and replacing the 65 amp alternator with a 120 amp alternator. My Bad.  

Edited January 28, 2018 by retiredmechanic74 (see edit history)

[joe_padavano]

3 hours ago, retiredmechanic74 said:

Just a heads up I studied OHM's Law and was only trying to give a simple answer to a simple question. And secondly the doubling of the 12 Gage wire is being controlled by a pulse-width modulator and has been in service for over 6 years now, exposed to the elements, and I failed to mention the solder joints, the 30 amp fuse and replacing the 65 amp alternator with a 120 amp alternator. My Bad.  

 

While doubling conductors will USUALLY work, the reality is that the resistance through the two will never be EXACTLY the same.  More current will flow through the wire with the lower resistance crimps to the connectors,  and the risk there is that you might then overheat that wire.  This risk increases as the installation ages and corrosion sets in.  Keep in mind that the fact that one has never hit a deer is not proof that deer whistles work.  Same thing here.  The fact that you've been lucky for six years isn't proof that your installation is completely safe. In my day job in the aerospace business people frequently like to claim that something they've done has been "flight proven" and thus will work.  I always point out that it took NASA 25 tries before they had a three sigma day with the space shuttle. That didn't end well.

[retiredmechanic74]

7 minutes ago, joe_padavano said:

 

While doubling conductors will USUALLY work, the reality is that the resistance through the two will never be EXACTLY the same.  More current will flow through the wire with the lower resistance crimps to the connectors,  and the risk there is that you might then overheat that wire.  This risk increases as the installation ages and corrosion sets in.  Keep in mind that the fact that one has never hit a deer is not proof that deer whistles work.  Same thing here.  The fact that you've been lucky for six years isn't proof that your installation is completely safe. In my day job in the aerospace business people frequently like to claim that something they've done has been "flight proven" and thus will work.  I always point out that it took NASA 25 tries before they had a three sigma day with the space shuttle. That didn't end well.

All well and true,but, after owning my own Auto Electric business for more then 16 years and building wire-harness's and modifying electrical systems  have given me the confidence I have. I also fused the system just in case. 

[Vila]

Sactownog

 

Yes, from what I have read the information in the other posts is correct.

 

With reference to your question on a different wire gauge for Positive ground 6V systems, the answers provided by others is correct in that there should be no difference wire gauge between Positive or Negative ground 6 Volt systems.

 

The difference in wire gauge has to do with 6 verses 12 Volt systems, not Positive verses Negative grounding.

 

For a 6 Volt system to provide an equal amount of "POWER" to a vehicle accessory (i.e. Starter, Lights, etc, etc) that a 12 Volt system would supply requires more AMPS (electron flow) for the 6 Volt system, thus the 6 Volt system would need larger wire then a 12 Volt system to handle the increased AMPS.

 

Use wiring sized for a 12 Volt system in a 6 Volt car and you run the risk of wires over heating.  Use wires sized for a 6 Volt system in a 12 Volt car and you should have not problems other than over kill and spending more money then required.

 

[Frank DuVal]

At the risk of taking this topic off course again.....   You guys stared it...

 

Paralleling of conductors is a common construction method in the electrical industry for high current circuits. Not many people like to pull conductors greater then 4/0 over long distances. Since most of this is hidden in conduit, no one notices, but take a look at the 500 kV lines and you will see parallel conductors up there on the insulators.

 

Any wiring method can be done right or wrong. Doing it right (connections, etc.) goes a long way to make it safe.

 

Also, in the motor rewinding business they parallel conductors when winding coils.

 

The rule for parallel conductors is the cross section area in circular mils doubles or halves for every three awg sizes. Need 10 awg, but don't have any? Two 13s and you are fine. Of course, except in enameled copper wire, odd awg sizes are not usually found under size 3, use two 12s. Hmm, that's what RM74 did!

 

And finally, 12 awg is good for 30 amps, as long as the terminals are rated for operating at 90°C !  It is the NEC that limits it to a 20 amp circuit for protection. But, you are allowed to use the 30 amp rating to perform derating for # of conductors in conduit, etc.

 

Back to the original question. Which post of the battery attaches to the chassis makes no difference on wire size. Duplicate the sizes currently in the harness. 

[jan arnett (2)]

I would do two things.  Go to a welding shop and get some "0" welding cable for connecting the battery.  Make absolutely sure that you  grind off all paint and rust where the cables connect and where the engine mounts to the frame.