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Wiring the brake light functions

kendelrio

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On my M725, it was partially converted to 12v, so I looked at the wiring harness to see if it was salvageable, and alas, it was not. It has a 12v 350 in it, and whoever did the conversion hacked it up electrically. There was a 24v generator hooked to most of the lights and a 12v alternator running the ignition on the engine.

My plan is to wire it myself, and I have puzzled myself into a fit.....

That said, I am building a loom, and I may be overthinking it, but heres my question(s):
Turn relay box: There isn't one, the previous owner has a simple three way relay with 5 outputs: indicator lamps on the turn lever, 2 left and 2 right. For the sake of not confusing myself, I'm going to use these terms: Tail light (normal, light is on), brake light and turn signal.

My question is assuming the switch is in the "Service Drive" position.

Looking at the diagram (I've included it as a photo for reference and a .pdf of you want a clearer image to download):

1000024361.jpg:

On my truck, power is sent to the tail lights via wire 21 to the taillights. I have power going to my turn relay with wire 467. I have already wired in the turn signals (22-460-461) to flash at the appropriate time with the taillights on. My issue is brake light signal. Based on what I see, when I apply my brakes, power will flow from wire 75, through the hydraulic switch, then back to 75A through wire 22, where in the schematic it goes to the relay box to activate the "Stop" side of the STOP/TURN function. I don't have the relay box, so how would I wire this to allow the brake function to work, but be interrupted by the "TURN" function?
 

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Barrman

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At least you have figured out the proper wires Ken. Most people don’t get that far.

You don’t have to re invent the wheel. Your HMMWV and big truck with the evil eyes you had at the rally last year both have the same blinker/stop light set up in them. With a military flasher box and blinker arm, you can make the same system for your M725. That is how I did the blinkers/stop lights for my M715. There is even a military harness meant to convert trucks over to the system your other trucks have. I got such a harness off eBay.

If you are determined to name your new round thing that rolls a wheel. Then you have it correct already. The brake light signal has to go through the blinker system. Not the other way around. The military system and the civilian Spartan made systems old Jeeps had both had the input wire (75A) for the brake signal go to the blinker arm. Then the blinker arm would send just a solid brake light signal out to the rear only or an intermittent to one side depending on blinker arm position.

So, your blinker arm is the brains of the set up and you didn’t mention what arm you have.
 

kendelrio

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At least you have figured out the proper wires Ken. Most people don’t get that far.

You don’t have to re invent the wheel. Your HMMWV and big truck with the evil eyes you had at the rally last year both have the same blinker/stop light set up in them. With a military flasher box and blinker arm, you can make the same system for your M725. That is how I did the blinkers/stop lights for my M715. There is even a military harness meant to convert trucks over to the system your other trucks have. I got such a harness off eBay.

If you are determined to name your new round thing that rolls a wheel. Then you have it correct already. The brake light signal has to go through the blinker system. Not the other way around. The military system and the civilian Spartan made systems old Jeeps had both had the input wire (75A) for the brake signal go to the blinker arm. Then the blinker arm would send just a solid brake light signal out to the rear only or an intermittent to one side depending on blinker arm position.

So, your blinker arm is the brains of the set up and you didn’t mention what arm you have.
This is what I'm working with. Its this style, but original.

Screenshot_20260213_054430_Chrome.jpg
 

marchplumber

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OK. Post 5 in this thread has wiring directions for what I think is that unit.

People helping people cause they can and want to! S.S. top three traits....people,assistance from people, broad knowledge shared by people........GOOD luck with the brake lights....as mentioned, dont reinvent wheel....youve got tons of experience.....like the "elephant meal", best way to eat an elephant is a single bite at a time
 

kendelrio

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I even did a video a year or so ago about testing a system similar to what you are messing with. The wiring set up in it might apply to your set up as well:

I appreciate you!

I found out it's a VSM 900 Signal-Stat

20260216_090030.jpg


and using Google lens, found this drawing.

FB_IMG_1771257808048.jpg

Then i was wondering why none of the colors matched, so I removed the electrical tape wrapped around it and realized someone in the past had swapped wire colors.

They all lined up perfectly when I realized that and got it working.
 
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