Early Cowl Battery Box Circuit Breakers

[Naugha]

Ron your last post is excellent and it demonstrates best practices in useful communication.

You supplied the right amount of background info on the topic so that the non-expert can join the party then you hit home with the most useful details and precautions..... maybe even prevented an unexpected zap.

Did you ever teach a 9th grade auto class ??
_________________
Don Alvarez
Retired HS Teacher
Central Florida
M38 Project

[RonD2]

Thanks for the compliment Don, appreciated. Nope, never taught 9th graders anything. Did teach some teenage Marines a thing or three back in the day. Does that count?

And reading between the lines....I do get carried away with some posts. Some folks fight obesity. I fight verbosity. I'll try to do better.

Usually Wes gets me back in line. Thanks!
_________________
Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

[Naugha]

I’m using the three old CBs to practice my Douglas connector and wiring skills. So far it’s looking good. The shells clean up nicely and the crimping tool works fine. I have 25’ of Prestolite wire to play with plus the smaller Douglas parts.

The new replacement plastic connector cylinders I bought are a little long but if you sand .5mm off each end they match the originals, which are actually very clean and could be reused.

The outside of the CBs and Doug connectors are rusty but clean up with a wire wheel and sandpaper ... the inside of the Doug units look amazingly clean. The wires are rotten but still have their number tags... pics later.

When finished I will take the rewired string of CBs to the local classic auto electric shop (the one that doesn’t do military) and have them attempt to smoke it.... something I just want to see.

Maybe they will smoke. Maybe they will trip, cool down and reset. Maybe run the test three times.

It’s like my U of F zoology research project with possum thermoregulation .... you got to grab ‘em by the back of the neck and stick a thermometer up their little arses to find out what is going on inside..... something Florida possums don’t like.
_________________
Don Alvarez
Retired HS Teacher
Central Florida
M38 Project

[wesk]

[RICKG]

[Naugha]

I was going to use my reloading tumbler but the shells were very rusty, had lost all their brass coating, just wanted to practice my Doug connector skills and then do a crazy test of the take off CBs. Besides... the shells are just a container and tensioner for the phenolic connector cylinder and are not part of the circuit ... right???

Here is some more stuff rattling around in my head.

* I’m using 14 gauge Presto for replacement wire ... but should that be 12G?

* The generally available NOS replacement CBs are 30amp but these take offs are 15amp as per the manual (I think) ... so what’s up with that ??? Are the 30 amp CBs a poor choice for replacing the 15amp CBs mounted on the cowl BB ?

* So, in an early M38 CB configuration, the #10 wire jumps across to all three CBs, then becomes wire #11.... with the small diameter connection on each CB going to various sub-units such as the light switch .... which depending on the switch used .... may/ or may not contain it’s own CB. Right??

I am leaning toward building an early M38 harness.... functioning BO lights, no turn signals. I plan to run this thing in the slow moving historic area / downtown square .... and on the desolate dirt roads that surround my Barn ... known as Black Sink Prairie .... a place so remote that you can’t get there from here.
_________________
Don Alvarez
Retired HS Teacher
Central Florida
M38 Project

[RonD2]

Pretty sure new shells are cadmium plated (not brass) for corrosion resistance. Taking that off could get the tin rusting faster, especially in damp-wet environment.
If the cad-plating is gone, maybe consider giving them a rattle-can spray of clear coat for protection?
Corrosion breeds more corrosion, and any corrosion around electricity isn't good. Just my 2-cent opinion.

Using a 30-amp CB in place of a 15-amp sounds like a good idea?

Recommend using the size wire gauge called for in the manual, which may or may not always be easy to decipher.

Could be mistaken, but think both early (triangular face) and late (oval face) light switches have built-in circuit breakers.
I don't recall ever seeing what the amp rating is, but pretty sure they're thermal auto-reset like the others.
_________________
Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

[4x4M38]

I would not go up in amperage on a circuit breaker for an original 24 volt figured vehicle.

Going up in amperage raises the point where the breaker trips.

FYI, in your modern vehicle, if you have a 10 amp fuse in a circuit that keeps tripping, do you try and find the problem or just stick a 20 amp fuse in there?

Just my two cents.
_________________
Brian
1950 M38
MC11481
http://www.willysmjeeps.com/v2/modules.php?set_albumName=album372&op=modload&name=gallery&file=index&include=view_album.php

[wesk]

The simple rule is: Thou shalt never exceed the posted circuit protection limit. The reason a 15 amp CB was used in those three positions was because it is the max current the engineers designed that circuit and harness to handle.
_________________
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

[Naugha]

Assuming some folks rebuild these things to 100% original specs, where does one find 15amp new/NOS CB's with Douglas connections?

Also. "Recommend using the size wire gauge called for in the manual, which may or may not always be easy to decipher." RonD

The pdf search function finds 50 hits for AWG in Ord 9 SNL G-740.
30 #14 / 10 #12 / 2 #16 / 2 #8 / 1 #10 / 1 #2 ... and a few I think were two or more wires in one hit)

So am I supposed to decipher those hits and cross my fingers I get it right or could someone just tell me the gauge of the wires attached to the cowl BB CBs ?

I was thinking they were all AWG 14 but a pic from the albums shows at least one #12 wire. Too bad the various wiring diagrams don't show the gauge of each wire but then that would be easy .... or is there a diagram that shows the wire sizes in the harness ???

BTW. When using the pdf search function for cable size I think I saw at least one ‘cable’ that was identified by its diameter rather than the AWG #, so when you rub the lamp .... try using a few different magic words.
_________________
Don Alvarez
Retired HS Teacher
Central Florida
M38 Project

[4x4M38]

Hi Don,
Yes there is a little deciphering, but it all makes sense.

The input wire into the breakers is #12, because it carries the load for all three circuits. Downstream of the breakers the wire is #14 like most wiring, as that gauge will handle the service for that circuit.

If you look the various wire sizes make sense given where they are used and what they are feeding.

Keep plugging along. We can help.

Brian
_________________
Brian
1950 M38
MC11481
http://www.willysmjeeps.com/v2/modules.php?set_albumName=album372&op=modload&name=gallery&file=index&include=view_album.php

[4x4M38]

As far as the connectors. You see wire 10 comes from the regulator and according to the diagram on page 1 it has a connector in it between it and the first breaker. When you make that wire from the connector to the first breaker put a Packard connector on the breaker side. Then make your jumper and downstream wires with Packard connectors at the breakers. That way you can use the breakers with Packard connections.

You will need to find two Klixon 15 amp 24 volt breakers with a double connector on the input side.

No doubt the motor pool guys used Douglas/Packard adapters like this as they maintained these vehicles over their life span.
_________________
Brian
1950 M38
MC11481
http://www.willysmjeeps.com/v2/modules.php?set_albumName=album372&op=modload&name=gallery&file=index&include=view_album.php

[4x4M38]

https://www.ebay.com/itm/224699217336
_________________
Brian
1950 M38
MC11481
http://www.willysmjeeps.com/v2/modules.php?set_albumName=album372&op=modload&name=gallery&file=index&include=view_album.php

[RonD2]

Don,
Call this guy and discuss what you want. https://vintagewiring.com/m-series/
How did he figure out wire gauge sizes? And I recommend the turn signal option. The Army adopted it. You'll be glad you did.

Can't find new or NOS 15-amp circuit breakers with Douglas connectors to tuck out of sight under the dash? Tip of the iceberg.
Have you found 24V headlights with Douglas connectors? https://www.oshkoshequipment.com/products/detail/10/1/Headlight-24V-Headlamp-Head-Light-Lamp-Bulb
https://memphisequipment.com/headlight-24-volt-with-douglas-connectors-p4099.html

Those Douglas to Packard adapters were made for a reason.
_________________
Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

[Naugha]

Excellent advice on solving the CB replacement problem. Thanks.

Back to the gauge of those CB wires. I could not read any markings on the rotten wires then decided to trim them back and make a direct measurement of diameters. Here is what I think I found.

Wire #10 & #11:
Wire #10 comes in from the VR then jumps across the three 15amp CB's where it exits as wire #11 which goes to the ignition switch. These wire #10 sections and wire #11 measure approximately .230" in diameter which probably makes them AWG #12.

Wire #25:
This wire comes off the 'first' CB ( the one that brings in wire #10 from the VR)... then goes to the horn. The diameter of wire #25 is approx. .180" which probably makes it AWG #14.

Wire #15:
This wire comes off the last CB and goes to the light switch. With a diameter of approx. .180 it is probably also a AWG #14.

Wire # (??):
The wire coming off the small Doug connector of the center CB is missing from my take off harness section ... so much for tag & bag. I am looking at 'early' wiring diagrams of the center CB but get lost in the 'dotted lines' ..... are we talking pig tail here... any help ???
_________________
Don Alvarez
Retired HS Teacher
Central Florida
M38 Project