Tracking a wire issue

[Charlie175]

Worked on Deuce 2 today getting the in tank pump freed up. It was gunked up bad but after a acid bath I got most of the crude out of the pump and it turned freely. Hooked it up to Deuce 1 (batteries are in that one) and it operated fine (Just plugged it in and turned on power).
Installed it back in Deuce 2 (Changed batteries to this one) but I have no power to the plug. This is wire 654. Tracing this wire I can see it going into the rear coupler and then from there its in the giant wad of wires. Any common locations that this wire wears or breaks?
It seems this same wire ties into the Oil Pressure gauge, and on this truck the gauge stopped working. The Air pressure buzzer works so it is getting power to that.

My understanding is you turn the main power switch on, this feds power to wire 27 which then feds to wire 654.

Thanks!

 

[DaneGer21]

Worked on Deuce 2 today getting the in tank pump freed up. It was gunked up bad but after a acid bath I got most of the crude out of the pump and it turned freely. Hooked it up to Deuce 1 (batteries are in that one) and it operated fine (Just plugged it in and turned on power).
Installed it back in Deuce 2 (Changed batteries to this one) but I have no power to the plug. This is wire 654. Tracing this wire I can see it going into the rear coupler and then from there its in the giant wad of wires. Any common locations that this wire wears or breaks?
It seems this same wire ties into the Oil Pressure gauge, and on this truck the gauge stopped working. The Air pressure buzzer works so it is getting power to that.

My understanding is you turn the main power switch on, this feds power to wire 27 which then feds to wire 654.

Thanks!

Maybe the actual plug is bad. I know mine was and I had to get a new one.

Could you maybe try to scratch some insulation off the wire and check for power BEFORE the plug end?

 

[Charlie175]

I can try that. Thanks for the suggestion. Where did you get a new one?
This is on my M756 so the tank is exposed to the elements all the time due to the shorter bed.

 

[Guyfang]

What model truck? What TM? Then we can look at the wire diagram.

 

[DaneGer21]

I can try that. Thanks for the suggestion. Where did you get a new one?
This is on my M756 so the tank is exposed to the elements all the time due to the shorter bed.

Here’s where I ordered mine. Although listed as the brake connectors, it’s also the same plug for the top of the fuel tank.

Military Truck Parts

M35A2 parts, 5 ton parts, M151, M37, CUCV, HMMWV, Hummer, Mutt, M818, M813, M923, M939,

www.realcustomtrucks.com

 

[Charlie175]

What model truck? What TM? Then we can look at the wire diagram.

M756a2
I was looking at the PDF wiring diagram someone did up for the M35

 

[davidb56]

Its floating around here somewhere. I even posted it once and now its gone off my pc.

 

[davidb56]

does this help? its not the colored one I had. https://schematron.org/m35a2-wiring-diagram.html

 

[davidb56]

or this. https://www.xm381.com/TMs_Files/WIRING SCHEMATIC.pdf

 

[Mullaney]

Worked on Deuce 2 today getting the in tank pump freed up. It was gunked up bad but after a acid bath I got most of the crude out of the pump and it turned freely. Hooked it up to Deuce 1 (batteries are in that one) and it operated fine (Just plugged it in and turned on power).
Installed it back in Deuce 2 (Changed batteries to this one) but I have no power to the plug. This is wire 654. Tracing this wire I can see it going into the rear coupler and then from there its in the giant wad of wires. Any common locations that this wire wears or breaks?
It seems this same wire ties into the Oil Pressure gauge, and on this truck the gauge stopped working. The Air pressure buzzer works so it is getting power to that.

My understanding is you turn the main power switch on, this feds power to wire 27 which then feds to wire 654.

Thanks!

.
Note sure about the M756a2 but I do have drawings of the electrical system for the Deuce.
Also have the list of Wire Numbers and what they connect to.

 

[Charlie175]

Yes that is the one I was looking at. The CAD file plot. I can trace it back to the rear wiring coupler but going forward it is in a large bundle of wires.

 

[DaneGer21]

Yes that is the one I was looking at. The CAD file plot. I can trace it back to the rear wiring coupler but going forward it is in a large bundle of wires.

You could use a multimeter at that coupler and check continuity from there to the tank to check for a broken wire and also a short to ground. Or from there forward you could check for a short to ground.

Maybe probe the wire at the start switch since it’s on the same circuit and check continuity from the start switch to the coupler.

 

[Mullaney]

Yes that is the one I was looking at. The CAD file plot. I can trace it back to the rear wiring coupler but going forward it is in a large bundle of wires.

.
Following the wire to the back - can you locate the "wire tag" number out back? If so, through the miracle of all the wires being the same color (not really - no miracle - just frustration) can only be wiggled out of the "clump of wires" up front is to wiggle and pull little bits at the time.

WHATEVER YOU DO, don't pull that wire out of the bundle!

In days gone by when a wire is bad or you just needed to pull another - using the existing wire to pull it. Either solder the new wire to the old or something better than a barrel connector. You don't want that bump to interfere with your pull... Wiggle a little slack in the direction you are trying to follow, pull some of the new wire forward and do it again. LOTS of wiggling to find that one dang wire - but short of a replacement wiring harness - that is the easiest way.

 

[Charlie175]

Thank you for the help!

 

[Guyfang]

.
Note sure about the M756a2 but I do have drawings of the electrical system for the Deuce.
Also have the list of Wire Numbers and what they connect to.

Who ever did the wire diagrams did an outstanding job! I attached a simple description of how the wires can be checked. From the pump to the Rear harnes connector, wire #654, output from the pump to the connector, Pin F. From the connector, pin F to the start switch, pin A. Where the wire changes from 654 to 74, is maybe a TB, Terminal board, or a three prong connector. But if you look under the dash, and trace the start switch pin A wire, (74) you should find it.

 

[Charlie175]

Looking at it closer, at the rear coupler, just forward of the connection someone had cut out the wires and redid the wires for about a foot section. Must have been damaged at some point.
The issue I see is 2 wires are broke off right at the connector but only 1 broken loom wire is present.
Second issue is I have 7 wires coming from the harness forward of the patch, I should have 8 per the diagram. I have 8 right at the connector counting the 2 that are broken. 1 of the broken wires is missing forward.
Also to understand the system, there is no fuse panel. What happens when a wire grounds while live? it just melts?

 

[davidb56]

.
Note sure about the M756a2 but I do have drawings of the electrical system for the Deuce.
Also have the list of Wire Numbers and what they connect to.

thats the one I was looking for and lost on my computer. I remember having to wear sunglasses to read it because the color is so bright. hahahaha too bad it couldn't put in the permanent threads like the TM's Guyfang did. I use his posts instead of my manuals, because its 3 times as fast. we owe a big thank you for his effort.

 

[Guyfang]

thats the one I was looking for and lost on my computer. I remember having to wear sunglasses to read it because the color is so bright. hahahaha too bad it couldn't put in the permanent threads like the TM's Guyfang did. I use his posts instead of my manuals, because its 3 times as fast. we owe a big thank you for his effort.

I think we could do just that. The ETM's that I uploaded are just big PDF files. Using a PDF program, you just open up the PDF, and insert another PDF file, and close it up again. I am not an expert. So maybe someone smarter then me can look at that? Mullaney?

Open to see comments.

 

[Guyfang]

Looking at it closer, at the rear coupler, (do you mean the Rear Harness Connector?) just forward of the connection someone had cut out the wires and redid the wires for about a foot section. Must have been damaged at some point.
The issue I see is 2 wires are broke off right at the connector but only 1 broken loom wire is present.
Second issue is I have 7 wires coming from the harness forward of the patch, I should have 8 per the diagram. I have 8 right at the connector counting the 2 that are broken. 1 of the broken wires is missing forward.
This is the tough part. It requires you to take the Rear Harness Connector off, find out what pins have broken off wires on them and then look at where that wire would go. Then disconnect those wires at the other end, and ohm them to the broke off wires, until you have continuity. Then you know what wire it is and where it goes. Time consuming, but that's what I would do. Or find a new/used but good front and rear wire harness.
Also to understand the system, there is no fuse panel. What happens when a wire grounds while live? it just melts?

Open to see comments

 

[Charlie175]

Update. Wire F at the rear coupler happened to be the broken wire. Cutting back some insulation I have power. Now to add a splice wire to the coupler. Just have to remember how to get the connector out of the plug.
I have continuance from the rear plug to the tank