Making a wiring harness

[fireguyfire]

So I’m going to soon get to the wiring harness on my 1940 1/2 ton, 6 volt. The original harness is there, but is in terrible shape with a lot of the cloth insulation missing, or falling off.

I am in western Canada, and by the time I pay the extra 30% in exchange and then shipping, an aftermarket harness will be over a grand for my truck, so I’ve decided to make a new harness as close to factory as I can.

The wiring diagram in my FSM is super basic, and doesn’t show wire gauges, colours etc.

Can anyone make any suggestions on how to go about best making a new harness for my truck?

[Young Ed]

See if you can find online or maybe in here a wiring diagram for an early 50s car. Those list the gauge. I did my 48 plymouth using the 1950 chart for size. The lighting was a mix of 16 and 14 but for simplicity and an upgrade I used all 14. Then there are a few thicker ones for stuff like the charging circuit. 

[fireguyfire]

I wish a guy could buy one of those colour wiring diagrams for my truck; I’ve used them on later trucks and a bunch of muscle cars I’ve restored and they are super handy.

[jsd245]

This site has PDFs with complete harness schematic including colors and lengths of wires. Yet I guess it’s just for the b series. 

 

http://dodgepilothouseclub.org/know/wiring_harness/

Edited February 19, 2022 by jsd245
Diagrams only for b series

[fireguyfire]

Thanks; this could still be very helpful as a basic how to and starting point.

Again I wish there was something similar out there for earlier dodge trucks!

[Eneto-55]

This is still a "work in progress" (because my job keeps getting in the way of my hobby), but I'm in the same boat on my P15.  Even once you have the colors & wire gauges, there is the question of lengths, to be able to total up how much wire you need of each type.  I have dismantled the entire forward part of the wire harness, marking various alignment reference points so that I can do the wrapping before installing it in the car.  The main reference points I designated are where it goes through the radiator side shield, and of course where it passes through the fire wall.  Then I also marked a couple of others that are rather arbitrary, so that there is one in any area between which any wire enters and exits the bundle.  Every wire at each of these points has a distinctive marking, so that I can get the wires back in the correct relationship one to another.  Then I've also measured each wire, and put this information in a spreadsheet with beginning and ending connections noted.  But some of the wires had been replaced or repaired before I got the car (in 1980), and others I had repaired back then myself.  So some of the length measurements may not be correct.  I figure I should still make the wires a bit longer at each end, and do the terminal connections after I have it installed in the car.

It's actually been quite a while since I have been able to work on this, and I hope I labeled everything well enough that I will understand the meaning of each label & marking when I am able to get back to it....

[B1B Keven]

Once you find the schematic, this is a great source for materials:

https://enginebarn.myshopify.com/

[fireguyfire]

Definitely looks like a good source for cloth covered modern wire.

 

is there an easy way to determine the gauge of my badly deteriorated original wires? I’m thinking if I strip the cloth sheathing off, which is falling off and use calipers to measure the diameter of the strand copper wire inside; is there a chart or something that I could use the diameter to convert to a gauge size?

Edited February 19, 2022 by fireguyfire

[fireguyfire]

I’m thinking that I will do what Keven suggested and get the main harness the same as the original as far as “splits” go, and leave an extra 6” on the end of each wire in the harness.

Then install the harness and make the lengths of the terminations perfect to where they are going. 

[Young Ed]

1 hour ago, fireguyfire said:

Definitely looks like a good source for cloth covered modern wire.

 

is there an easy way to determine the gauge of my badly deteriorated original wires? I’m thinking if I strip the cloth sheathing off, which is falling off and use calipers to measure the diameter of the strand copper wire inside; is there a chart or something that I could use the diameter to convert to a gauge size?

Just use that pilot house diagram. I'm sure everything would carry over except lengths. 

[Eneto-55]

1 hour ago, fireguyfire said:

Definitely looks like a good source for cloth covered modern wire.

 

is there an easy way to determine the gauge of my badly deteriorated original wires? I’m thinking if I strip the cloth sheathing off, which is falling off and use calipers to measure the diameter of the strand copper wire inside; is there a chart or something that I could use the diameter to convert to a gauge size?

That's another thing I did - count the strands.  That will also tell you the gauge, if compared to data from known MoPar wiring.

If the cloth covering is good enough inside the wrapped part of your harness, you can also go by the number of strikers (tracers) on the wire.

[lostviking]

Take a look at Page 129 in the shop manual. It shows the diagram including the gauge and color.

[fireguyfire]

Page 129 in my FSM is in the middle of the engine section.

My FSM is the Dodge truck shop manual

1940 series

VC,VD,VF,VG,VH,VK,VL,VM,VKD,VLD.

 

Do you have a different manual than that lostviking?

[fireguyfire]

Is there a rule of thumb out there regarding the number of strands in a wire, and the gauge?

[Merle Coggins]

[fireguyfire]

Perfect, thanks!

[LMBoise]

I am currently creating a harness for my ‘48B using the extensive PDF file located on this site. It has all of the colors, lengths, gauge as well as connection types. While yours is probably different, what I have done is put the main harness together leaving extra room on each end of all the individual wires and then taping the wires together at the various branches. I then dry fitted the harness in the engine bay prior to wrapping it to see if I got the various branches correct. By having each of the branches just tapped together, I can make adjustments as needed. I got all of my supplies from Rhodesia Island Wiring Service. They were great to work with, had an amazing inventory  of cloth wire and all of the connections. 
 

Not sure if this will work for you but may be an option. 

[LMBoise]

Oops, dang auto correct. It is Rhode Island Wiring Service. 

[rockingjd]

I have rewired both my Fargo and my wife's 53 Doge car. The cloth wire would be nice for originality but I didn't use it. I did use a black fiber loom from a company called Techspan. Run loose wire where you want it to go. From the dimmer switch to the head lights for instance. I ran wire loose for the entire truck then pulled it into the loom. Where one loom meets another and forms a Y I used black cloth hockey tape to cover up the joint and hold the two looms together. It is a large undertaking. Think 1 circuit at a time and you will get it done.

 

https://techspan.ca/details/techspan-automotive-loom-tubing-fiber-loom-769805-fiber-loom-2032

 

Edited February 20, 2022 by rockingjd

[lostviking]

17 hours ago, fireguyfire said:

Page 129 in my FSM is in the middle of the engine section.

My FSM is the Dodge truck shop manual

1940 series

VC,VD,VF,VG,VH,VK,VL,VM,VKD,VLD.

 

Do you have a different manual than that lostviking?

I have the reproduced Dodge Shop Manual. It covers all W series trucks. I got mine at RockAuto. I thought yours was a 1940 WC, so that manual isn't the right one for your truck.

Edited February 20, 2022 by lostviking

[lostviking]

15 hours ago, fireguyfire said:

Is there a rule of thumb out there regarding the number of strands in a wire, and the gauge?

Finer strands means of course more, but the same current capacity. The finer strands allow the wire to bend easier, without breaking stands. Think about trying to bend a rod. One side is being squished together, the other ripped apart. The finer the stands, the less distance between the two edges, the less stress difference.

[lostviking]

BTW, you should get the parts manual also. They sell both at RockAuto and I'm sure other places.

[fireguyfire]

I’ve got both the shop manual and the parts manual for my 1940 VC.

 

[lostviking]

My bad. I see the W series started in 1941. 

Edited February 20, 2022 by lostviking

[Eneto-55]

19 hours ago, fireguyfire said:

Is there a rule of thumb out there regarding the number of strands in a wire, and the gauge?

There is a formula to determine the gauge of stranded wire, something like strand diameter x number of strands, but what I was talking about is being able to determine the gauge of a wire that has such deteriorated insulator/covering that the strikers can no longer be clearly seen.  I thought that I had recorded the relative strand numbers for each gauge wire incorporated in my 46 P15 original wiring harness, but if I did, I can't find the file now.  But I DID do strand counts to compare the different wires, to be sure of the gauge of some wires that were so faded or frazzled that I could not see the strikers at all.

 

It isn't a general standard, just relative to a given vehicle model (assuming that the manufacturer used the same quality and strand count for the wiring in all of their different plants).  As Lost Viking said, the strand count can vary for the same gauge of stranded wire, and the finer the strands the more flexible the wire will be, and the more resistance it will have to breakage due to flexing during normal operation of the vehicle.  (For instance, the same gauge stranded wire intended for vehicle use will have a much higher strand count than electrical wiring used in construction.)  So I've noticed that the cheaper automotive wiring has a lower strand count - heavier strands - than the higher quality (and much more expensive) automotive wiring.  If a supplier doesn't give the strand count, then buyer beware. (My opinion, at least.)

 

I may still find where I had recorded all of this, but here's an example:

The high beam wire is 12 ga, and has 41 strands.

The low beam wire is 14 ga, and has fewer strands.  (I compared the headlight wiring harnesses from my 46 & 49 P15s, and they are the same strand counts for each wire.  Those front harnesses are up at my shop, and so I cannot give the exact count on the low beam wire now, and the low beam wire on my main wiring harness is not so deteriorated that I had been able to count strands.)

The heaviest wire to the horn relay is 10 ga, and has 65 strands.

I did this strand counting initially in order to confirm what info I had found from a member here regarding the relationship between number of strikers and wire gauge, and also to help determine the correct wire gauges, since the wiring diagram for the P15 is not labeled with the gauges.  I was also trying to determine if the wire I was looking at purchasing was of a similar strand count as that originally used.  My understanding is that a finer strand wire is OK to use, but it would not be advisable to use a wire that used strands of a much heavier diameter (and thus a much lower strand count for a given gauge), such as using stranded house wiring.  (Not good.)