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willysmjeeps.com :: View topic - M38A1 Wiring Harness Alternative?
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M38A1 Wiring Harness Alternative?
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w30bob
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Joined: Mar 22, 2017
Posts: 160
Location: Great Mills, MD

PostPosted: Thu May 18, 2017 7:04 am    Post subject: M38A1 Wiring Harness Alternative? Reply with quote

Hi Guys,

I've decided to replace my main wiring harness in my A1, as it's a total mess. Between all the splices, changes, mods, etc there's really not much of the original harness left, and what there is is brittle and cracking. I'm not real fond of forking out many hundreds of dollars for a few wires and Douglas connectors, so I was looking at using a NOS M170 main harness as a starting point. Seems that most everything is there, as the A1 and 170 are the same, just different lengths. I see those harnesses for sale for $150.

But then I started looking closely at the wiring diagram for the A1 and noticed how familiar it is in comparison to my M37 wiring diagram, which I know by heart. So what I'm wondering is............could I use an NOS M37 harness in my M38A1. Both vehicles use the same electrical components but at different distances away from the light switch. But the M37 wiring should be longer to all components, not shorter.....so no issue there. I can hide any extra wire length by taping it into the harness. I've got tons of NOS M37 harnesses, both for the 2 plug and 1 plug light switch, so maybe this is a cheaper, easier way to go. I've got a few new regulator harnesses from the 60 amp kits that I can customize in length....so no problem there either. I will need to make a headlight harness for the A1, but I've got other junk harnesses that I can use for that.

So my question is...........does anybody see anything majorly wrong with using an M37 main harness as a starting point to replace my A1 harness? Am I overlooking something?

thanks,
bob
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wesk
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Posts: 12976
Location: Wisconsin

PostPosted: Thu May 18, 2017 10:54 am    Post subject: Reply with quote

Not a problem. Most of the older M series harness' are easily adapted. I have used old M35 harness' for my m38 and m38A1 in the past. I have a current M38 I am installing an M35 harness in now.

Since you mentioned the tons of M37 harnes you have, my 54 M37 is in need of a new harness. Are you willing to part with one?
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php
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RonD2
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Joined: Oct 02, 2014
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Location: South Carolina, Dorchester County

PostPosted: Thu May 18, 2017 9:43 pm    Post subject: Reply with quote

I second that. Will you part with another? I can PM if you'd rather take it off line. Please let me know.
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Ron D.
1952 M38,
1951 M100, Dunbar Kapple 01169903, dod 5-51
1954 M100, Dunbar Kapple M750759, dod 1-54

Album: http://willysmjeeps.com/v2/modules.php?set_albumName=album404&op=modload&name=gallery&file=index&include=view_album.php
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w30bob
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Joined: Mar 22, 2017
Posts: 160
Location: Great Mills, MD

PostPosted: Sun May 21, 2017 8:35 am    Post subject: Reply with quote

Hi Guys,

Sorry for the delay in reply.....weather has been too nice to be inside. I may have misspoken when I said "tons".....I've got probably 5 or 6 that I've picked up for my M37s over the past few years. When I can get to those harness I will sure look and see if I can spare a few, but a few words of warning. I bought my first M37 about 5 or 6 years ago and being new to MVs didn't know if wiring harnesses were available or not. Thinking they might be hard to come by I started buying them when I found them. When I installed one I quickly realized that these NOS harnesses are OLD. Meaning they look pristine until you install them and expose them to the elements. Then they start to dry and crack at a very rapid rate and you'd be lucky to get a few years out of them if you're lucky. We're talking rubber insulation that's in some cases 60 years old.

I've decided that I'm going to make all new harnesses from scratch for my M37 using an NOS harness as a pattern, and use the latest automotive wire, which will outlast me. I just haven't found the time to do it yet. I also have a little organization problem with my parts. I can tell you what room they're in, just not where in the room. And it's a big room.

Bottom line is yes, I can probably part with a harness or two, but you'll have to bear with me until I can find what I've got. If you're in a hurry you're best bet would be to contact Brian Asbury. I got a lot of my electrical stuff from him and he's got M37 harnesses last time I checked. He gets around $200 for an NOS one and is a top notch guy. You guys probably know him already. If not PM me and I'll give you his contact info.
Again, sorry for the delay.

thanks,
bob
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wesk
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PostPosted: Sun May 21, 2017 10:22 am    Post subject: Reply with quote

Quote:
He gets around $200 for an NOS one
Are these the same NOS you have that have well exceeded their shelf life and crack & crumble quickly when exposed to the atmosphere?
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php
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w30bob
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Joined: Mar 22, 2017
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Location: Great Mills, MD

PostPosted: Mon Jun 05, 2017 12:21 pm    Post subject: Reply with quote

Probably yes, but I don't know the date of manufacture of the harnesses he has. I just bought an NOS M170 harness to use as a pattern for my A1 and it was made in 1980 or 1981 (I saw the date on the wire yesterday, but can't remember which it is). It looked ok to use until I looked closer. All the rubber grommets in the connectors were cracked and falling apart. Once they go the conductor can make contact with the shell, which can make contact with the body and you know how that ends up.

Actually Vintage Wiring had a problem last year with the grommets in their Douglas harnesses falling apart within a year of purchase. Some folks over on G741.com came pretty close to losing their trucks. I assume they got that resolved by now, but those grommets are important. I can see why the Military switched to Packard connectors.

regards,
bob
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4x4M38
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Joined: May 30, 2014
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PostPosted: Mon Jun 05, 2017 2:03 pm    Post subject: Reply with quote

John at Midwest Military has very good prices for all of those parts.
You said you'd build a new M37 harness using new automotive wire.
You can buy reasonably new military spec wire which will allow you to use
the Douglas of Packard connectors. You will have some trouble matching
civvy wire up to the Douglas fittings.
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Brian
1950 M38
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w30bob
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Location: Great Mills, MD

PostPosted: Mon Jun 05, 2017 9:19 pm    Post subject: Reply with quote

HI Brian,

Yup, you're right......the problem with modern automotive wiring and Douglas connectors is that newer wire uses much thinner insulation than the old Auto-Lite or Prestolite wiring. So to have the Douglas connector shells fit properly you need to use new 12 ga wire, which is the same OD as the old 14 ga wire. BUT then you have to deal with the thicker conductor fitting in the connector pin. But the newer wire is so much better at temperature resistance and overall durability it's worth the effort. It also only comes with glossy insulation.....so a little Scotch Brite is in order to dull up what's not covered by electrical tape.

Regards,
Bob
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4x4M38
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PostPosted: Tue Jun 06, 2017 5:29 am    Post subject: Reply with quote

25 cents a foot for 160 feet plus five new Douglas connectors
and a trailer side connector:

http://m.ebay.com/itm/WIRE-HARNESS-W-DOUGLAS-CON-FOR-PARTS-5EA-WIRES-32-LONG-NSN-2590-00-534-2352-/331767569024?hash=item4d3ee35a80%3Ag%3A6DMAAOSwa-dWkrjs&_trkparms=pageci%253A03eae24f-4aaa-11e7-bba7-74dbd1807b59%257Cparentrq%253A7d2198db15c0a9c0b9281538fff910a2%257Ciid%253A3
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Brian
1950 M38
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wesk
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PostPosted: Tue Jun 06, 2017 7:13 am    Post subject: Reply with quote

I must agree with bob. Rather than risk an electrical fire using all the ancient NOS wiring I would use new commercially available wire.


This is the Ebay listing Brian postedfor a semi-trailer, stake M127A1. 1974! 43 years ancient!

This has turned into a discussion of old vs new. So that part of the discussion is the simple part. Old NOS can be original and nice looking but presents a great electrical fire risk. Acceptable only for display purposes. New presents sizing issues and can become risky when you use much larger wire cores than the circuit demands just for outer diameter considerations to fit terminal parts. What does this mean?

The engineers select wire gauge based on system current needs, operating voltages and length of runs. The amperage or wattage of the item powered will determine the gauge needed from 0 feet to a certain length need. As length gets over the first foot limit then you must go to the next heavier gauge. This keeps the wire adequate for the load and compensates for length of the wire run. This insures safety under load and still maintains the lightest possible weight. In the event of a short using the minimum acceptable gauge insures the resulting wiring damage will be minimal. This is because the heavier gauge wire can carry more current so when a short occurs the heavier gauge wire will reach the higher temperature resulting in a sooner fire.

The "bigger is better" analogy is not a wise one to use here. In Bob's case using the 12 gauge wire where 14 or 16 is called for will fit nice but will burn sooner and hotter when a short occurs. Even if he elects to add fuses or circuit breakers to his system it will cost him more since not only does the circuit load determine fuse or breaker capacity but length and gauge of the wire must also be factored in. The use of 12 gauge to replace 14 or 16 will result in a need for much larger fuses or breakers.

The better solution is to keep the circuits on your truck as original as possible using the correct required gauge wire with or without added circuit protection. If you shop the electrical wiring market you can find heavier insulations used for wire that must be shielded from outside heat and higher than normal abrasion. Select the correct gauge wire with the heavier insulation for your new military harness. If a case exists where the overall wire diameter is still a wee bit small where it enters your Douglas connector just add a layer or two of heat shrink at that point.
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php
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w30bob
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Joined: Mar 22, 2017
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Location: Great Mills, MD

PostPosted: Tue Jun 06, 2017 7:31 am    Post subject: Reply with quote

Hi B,

Yup........there's at least 3 such harnesses on Epay I've found, but although they're "new" the wire is over 40 years old and never exposed to UV or the elements. I wouldn't expect it to last very long once put into service, but I could certainly be wrong.

Now since you can't re-use the Douglas connector pins and the grommets probably need replaced......it might be cheaper to buy new Prestolite wire by the foot from guys like Saturn as well as new connectors. Unless you want to use the old hardware in the donor harness and have a million splices in your harness. Sort of 6 of one, half a dozen of another.

I'm going to look into what it would take to make the grommets in silicon, but it might be cost prohibitive when all is said and done. Maybe Packard is the way to go!

Thanks,
bob
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4x4M38
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PostPosted: Tue Jun 06, 2017 8:01 am    Post subject: Reply with quote

Wes,
The trailer harness I received from Saturn Surplus does not appear
to be 43 years old. In my hand it is very close in feel and appearance
to the M35 harnesses we bought. The sheathing is soft and pliable,
and the grommets are similar.

I've seen various older wiring examples that are dry, dull and crispy.
This wire is anything but. I am convinced it is newer replacement wire.

In any case, recent manufacture military wire and grommets are available.
I recently bought Douglas parts from John and his grommets are
fresh and new.

Just my opinion.
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Brian
1950 M38
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wesk
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PostPosted: Tue Jun 06, 2017 8:51 am    Post subject: Reply with quote

If you are buying NOS MilSpec wire from a surplus dealer then you should be able to confirm the dating off the packaging. If it is repacked by the dealer to bury it's history then don't be surprised if a year after you expose it to the elements that it deteriorates rapidly. If the dealer is above board then he should be able to answer any questions you have about dtaing of the original packaging. Try to keep in mind thru all of this that items of supply prone to age on the shelf were often re-opened by the Army supply folks, inspected and repackaged & redated!
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php
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4x4M38
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PostPosted: Tue Jun 06, 2017 9:49 am    Post subject: Reply with quote

All good points.
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Brian
1950 M38
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RonD2
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PostPosted: Tue Jun 06, 2017 2:10 pm    Post subject: Reply with quote

Is there a known good harness pattern drawing available for the M38? Willys must have had one in their drawing package?

I figure it's either that or buy a couple of 4x8 sheets of plywood and a box of nails to mock up a harness with a tape measure on the jeep. Then take some photos and draw it on paper.

I wasn't inclined to buy a NOS harness just to use for a pattern, but having one could save a lot of time instead of making one cold from scratch. Maybe I could borrow or rent a NOS harness for a week just to copy the pattern?

From what I can see, there's plenty of brand new fresh mil-spec wire available on the market for reasonable cost.
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Ron D.
1952 M38,
1951 M100, Dunbar Kapple 01169903, dod 5-51
1954 M100, Dunbar Kapple M750759, dod 1-54

Album: http://willysmjeeps.com/v2/modules.php?set_albumName=album404&op=modload&name=gallery&file=index&include=view_album.php
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