Wiring help, seeking wisdom

[jahrafa]

Hello,

I am currently working on a project restoring my 1952 M37. Working on making it street legal first , so that I can have fun and make sure it is solid, and then will tco body work and paint so that it looks nice. No sense in having a nice looking truck that does not drive.

Anyway, I am having a hard time wiring it. I purchased a front wiring harness that was not specified as for early or late model. I assumed it was similar with the difference of the turn signal wiring. My main problem is that I am having a hard time installing it, meaning which side each end of the harness goes to, except the light switch plug of course. One side splits three ways with one of the looms that I can identify is for the horn and temp sender wires. The other side just has several shell connectors.

The other issue I find is that every post about wiring diagrams I see, when I compare the numbers of the wires, I see some numbers with letters on my harness that do not match the diagram. and the diagrams do not show which side of the truck the wires are supposed to go.

Can someone share some wisdom please?

Thank you in advance!

Rafael

 

[Mullaney]

Hello,

I am currently working on a project restoring my 1952 M37. Working on making it street legal first , so that I can have fun and make sure it is solid, and then will tco body work and paint so that it looks nice. No sense in having a nice looking truck that does not drive.

Anyway, I am having a hard time wiring it. I purchased a front wiring harness that was not specified as for early or late model. I assumed it was similar with the difference of the turn signal wiring. My main problem is that I am having a hard time installing it, meaning which side each end of the harness goes to, except the light switch plug of course. One side splits three ways with one of the looms that I can identify is for the horn and temp sender wires. The other side just has several shell connectors.

The other issue I find is that every post about wiring diagrams I see, when I compare the numbers of the wires, I see some numbers with letters on my harness that do not match the diagram. and the diagrams do not show which side of the truck the wires are supposed to go.

Can someone share some wisdom please?

Thank you in advance!

Rafael

.
Hi Rafael,

Mine is a 1954 and I honestly can't tell you if it is early or late. I did a quick search and found a couple of wiring diagrams in my stash. See if these are different from what you have maybe? Mine lives in a container, so if you need to see something - maybe something I could take a picture of - just let me know.

Pictures might help too if you can post a few.

 

[jahrafa]

.
Hi Rafael,

Mine is a 1954 and I honestly can't tell you if it is early or late. I did a quick search and found a couple of wiring diagrams in my stash. See if these are different from what you have maybe? Mine lives in a container, so if you need to see something - maybe something I could take a picture of - just let me know.

Pictures might help too if you can post a few.

Mullaney,

Thank you very much! great help. The schematic 001 looks similar in comparison with my harness. I appreciate your wisdom.

Question, maybe you can take a picture of the break switch wires? how are they connected on to the switch? it looks like two separate wires but with one double shell. Ussualy those double shells are for the 2 to 1 wire splits.

Thank You again!

 

[Mullaney]

Mullaney,

Thank you very much! great help. The schematic 001 looks similar in comparison with my harness. I appreciate your wisdom.

Question, maybe you can take a picture of the break switch wires? how are they connected on to the switch? it looks like two separate wires but with one double shell. Ussualy those double shells are for the 2 to 1 wire splits.

Thank You again!

.
Good! Glad the schematics helped a little.
I will see what I can do about a picture or two.

.

 

[M37keppy]

The brake light switch is 2 pined in one shell. There are military vehicle parts vendors that stock the switch with the dugless connector.

 

[jahrafa]

The brake light switch is 2 pined in one shell. There are military vehicle parts vendors that stock the switch with the dugless connector.

Thank you! It gets frustrating. As I kept researching, I was able to somewhat identify which end goes to which side of the truck. Then I found that the wires that go tothe brake light switch 75 and 75A and the one that feeds the dimmer switch 21C are on the oposite side of where they should go, they branch to the passenger side of the harness . is there a reason on just a fluke?

 

[G744]

The temp & oil senders, Bendix regulator plug, horn, and the dimmer switch wires come out on the driver side, and run down along the firewall.

If I remember rightly, the brake light switch wires come out on the passenger side, then connect to the rear loom along with the rear lights and fuel sender. The brake light wires then are run along the front transfer case support.

 

[jahrafa]

The temp & oil senders, Bendix regulator plug, horn, and the dimmer switch wires come out on the driver side, and run down along the firewall.

If I remember rightly, the brake light switch wires come out on the passenger side, then connect to the rear loom along with the rear lights and fuel sender. The brake light wires then are run along the front transfer case support.

That is awesome! Thank you everyone for the help! greatly appreciated

 

[booze_rooster]

Do you have a multimeter that does continuity? You can hook up the things you know, pin out the contacts and label what rings back to a switch terminal or connector.

 

[G744]

All the original wiring is the same color, black. Each end has a small aluminum tag attached with alpha-numeric designations for purpose. The code is the same for virtually all US 24V tactical vehicles and is listed in many TM's (especially the M37 series) that makes electrical connections easy to figure out.

 

[G744]

I just thought there is another possibility...you have wiring looms not for your truck...

 

[Floridianson]

Thank you! It gets frustrating. As I kept researching, I was able to somewhat identify which end goes to which side of the truck. Then I found that the wires that go tothe brake light switch 75 and 75A and the one that feeds the dimmer switch 21C are on the oposite side of where they should go, they branch to the passenger side of the harness . is there a reason on just a fluke?

Been a while but if I remember the two tail lights do not match if original. I had to run a separate wire from the passenger side from the passenger side wheel well. Was it the passenger side was just black out and riding lights no brake light so two different light housing?

 

[Gardy90]

Im just now seeing this as i havnt been active online in a good bit, you know how work and those projects around the house go. Anyway, i just rebuilt my whole trucks wiring harness from scratch over the winter. In the course of doing so I documented alot and made some edits to the schematics to be a little easier to follow. While the schematics will give you a working end result they dont show the full picture for what is in the vehicle especially if you have a more original harness from an earlier model truck. The only slight difference that i did to this harness(1952 original) i built was included the turn signal wires into the main harness where they were only included in the main harness on later models. I am slowly working on a writeup with plenty of pictures but in the meantime if you still are needing help let me know and ill see what i can do. After rebuilding it from scratch using the old harness as a pattern i know it in and out pretty well.

 

[G744]

Early M37's only had one stop/tail on the left. BO stop/marker on the right.

Later trucks had two stop/turn/tail, with an additional housing like the front BO's on a Jeep.

 

[Gardy90]

Early M37's only had one stop/tail on the left. BO stop/marker on the right.

Later trucks had two stop/turn/tail, with an additional housing like the front BO's on a Jeep.

Right, if I’m not mistaken that was with the addition of turn signals that the internals were changed out for a 3 wire, with 3 bulbs, and the B/O stop light added outboard of the passenger tail light.

 

[G744]

Yep.

Tho it was usually done by just changing out the entire taillight.