Civy truck to MIL trailer wiring info

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emmado22

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All,
This is some helpful info on building a trailer wiring "connector bender" for towing a MIL trailer equipped with the standard military harness/plug with a civilian type vehicle equiped with a 4,6, or 7 wire towing harness. This "connector bender" allows you to keep the stock wiring in your tow vehicle and trailer, and not alter either. Be mindful of 12/24V voltage issues. The Trucklite Omnivolt lights are a good way around this problem. Truck-Lite - Catalog Product : Rear LED Composite Lamps They are for sale on Ebay from time to time.

This same info can be used to make a "mil tow vehicle to civy trailer" connector bender also, just change the ends.

Obviously, using a civilian tow vehicle will not have blackout lights, nor will a civlian trailer towed by a MIL truck, and they are not discussed here, nor is parts suppliers.


Here is the info you need to know.

Civilian trailer wiring

Green wire = Right turn/stop light
Yellow wire = Left turn/stop light
Brown wire = Tail/marker/running lights
White wire = Ground

Military harness circut # and Pin
22-460 Pin J = Right turn/stop light
22-461 Pin B = Left turn/stop light
21 Pin E = Tail/marker lights
90 Pin D = Ground

Important note: Do not use circut 37/Pin K for a ground. Many times it is terminated and not connected to the trailer chassis. Circut 90/Pin D is ALWAYS the mil trailer ground.

Additional info on the civilian end of it can be found here:
Trailer Wiring Diagram For 4 Way, 5 Way, 6 Way and 7 Way circuits


A "diagram" of sorts of how it looks schematically is as follows:
Function Civilian 4 wire - MHC# Pin Letter in plug

Right turn/stop light Green wire - 22-460 Pin J
Left turn/stop light Yellow wire - 22-461 Pin B
Tail/markerlights Brown wire - 21 Pin E
Ground White wire - 90 Pin D

MHC# = Military Harness Circut # (small metal wire bands ID'ing wire)

The electrical receptical in the picture is an MS75021-2
One of the many manufacturers for this is BMI #870126B

They are frequently found on ebay, at MV parts houses, and on the back of every US Military MV that has an M series #. I like to buy cheap used/old MV harnesses on ebay, and MV shows as they are always good for sources of wire, connectors, cannon plugs, pins, and these recepticals.

One note on the receptical. There are 2 "ridges" on the receptical that keep the trailer's plug in tight. Sometimes you may need to sand them down a bit with a wire wheel so it is easier to get the plug on and off, but dont do it too much or else the plug will fall out. A little at a time is the way to go.

UPDATED INFO:


If you have a military pigtail coming off your trailer, here are the color codes that correspond to the wire circut numbers. The wire colors are the indiviual wires that are INSIDE the outer black rubber insulation.

24-484
22-461 LEFT TURN/BRAKE RED WITH WHITE TRACER
24-483
21 MARKER LIGHTS RED
23
90 GROUND BLACK WITH RED AND WHITE TRACERS
22-460 RIGHT TURN/BRAKE BLACK WITH RED TRACER
37
 

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clinto

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Anybody know the secret to copying picture from posts now? Wayne
Right click on the image, choose "open in new window". New window will open, save to your hard drive, voila.

:D
 

clinto

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Thank you for taking the time to write this up and post it.

:beer:
 

ida34

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As a side note, I added a civy connection to my M101 but wanted to retain the military connection. Instead of making a conversion cable or connector I went a different route. I had some mil spec connectors I got off ebay that gives a tap off a connection. I put them in where the trailer harness connects to the cable assembly. I then attached a standard four pin trailer connection to the taps. Now I have two cables on the trailer. One for the cucv and one for my civy trucks. Of course I changed the bulbs to 12 volt. The information above would have come in real handy when I did it. Thanks for posting.
 

Militoy

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Helpful info. I bought a "ready-made" version at the Papago MV Show auction in Phoenix last month. It's a sealed box with both military and civie covered female recepticles installed. It allows hooking up a military trailer to a civie truck - or the other way around, using just the standard pigtails. The $15 I paid was less than the parts would have cost - and no labor involved.
 

50shooter

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This thread is well timed. We are picking up a M105A2 next week and plan to use a Civi Chevy Silv. Is there any "gotchas" to watch out for? I've read several posts about the brakes and single v/s double line but I'll admit I don't know squat about these trailers as this is my first.

I'm assuming the truck will still have enough brakes to stop the empty 105...any thoughts?

Would it be easier to just run two brake lights to the back of the 105 and secure them some way then run the wires up to the 4 way?

Thanks for the help.
Jason
 

Militoy

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Got a picture of that, Militoy?
I could snap a photo in the morning - I'm a little too lazy to drive out to the back of my property tonight, and dig through my conex box - but I have to be there tomorrow. It's nothing fancy - just the 2 connectors mounted in the box, and wired up pretty much as shown above. How hard is it to post a pic without uploading it to my own webspace?
 

Sumoman

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Mine had no wiring to speak of and I was quoted about 750 to re-wire the whole thing, add LED, get the brakes working, etc. I thought that a bit high so I have held off.
 

charlietango

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good to have that harness explained

my question is there an answer to miltruck with civi trailer while keeping the trailer 12V'
i already have the 24-12V inverter which solves 12v brake controller but does not convert multiple functions like signal , brake , and running lights at once
 

Militoy

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good to have that harness explained

my question is there an answer to miltruck with civi trailer while keeping the trailer 12V'
i already have the 24-12V inverter which solves 12v brake controller but does not convert multiple functions like signal , brake , and running lights at once
There are a couple of ways I can think of to do that. One way would be to build a little module with a 3-terminal regulator like a 7812 in line with each 24V circuit, to drop each line to 12V as it is needed. 7812's are good for around 1.5A each - so you would have to keep the load on each individual line down to around 15W max. The other way would be to use your 24V-12V DC-DC converter, and run a 24V relay off each trailer circuit on the truck, to feed 12V from the converter to each lamp circuit on the trailer as needed.
 

charlietango

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thanks mili the 2nd option sounds good and easy.. just retrofit a fuseblock and relay pack to that converter i guess and steal feeds from the devices to make a new trailer harness for the truck.
i dont know what a 7812 is but i worry the amps on the brakes might be high... although doesn't the brake controller regulate that? ii have it running 12v already and can just run its own line to the trailer so that 7812 just needs to work off lamps ?


emmado i thought of that but still doesnt solve 12V electric brakes
 

ecostruction

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I'm wiring up a Civy trailer tomorrow for Military lights so I can hook to either. So I'll have two harnesses. One civy, one military. I'll then plug in the civy connection to my military harness to get the brakes only. So I'll have the standard military plug on the trailer, and just back from that I'll have a 6 pole receptacle wired into the MV harness that I can use to plug the civy connection into to get the brakes. Lights will be 24 volt deuce lights and bakes will be 12 v. When I want to pull with a civy truck, just unplug the 6 pole from the MV harness, plug into vehicle, then go.

Now, only getting the prongs correct on the MV harness and receptacle. The diagram above doesn't match the deuce. Number of pins correct, but the diagram above has them in a different arrangement than what i've gound. I have 12 pins, but they are in 5 rows as follows:
row 1 - * *
row 2 - * * *
row 3 - * *
row 4 - * * *
row 5 - * *

row 1 right pin is Right Turn
row 2 left pin is Left Turn
row 5 Righ Pin is tail/running lights/ and possibly brakes?

That's what I found using a tester. Don't know how to verify ground. Any thoguhts?
 

Militoy

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...i dont know what a 7812 is but i worry the amps on the brakes might be high... although doesn't the brake controller regulate that? ii have it running 12v already and can just run its own line to the trailer so that 7812 just needs to work off lamps ?...
The 7812 is a simple voltage regulator IC in a TO-220 package. It looks like a transistor with a hole in it for mounting, and has only 3 leads - input, output, and ground. You ground one pin, put anywhere from 14-32 volts into one end, and 12 volts comes out the other end. It has to be properly heat-sinked, and the more common non-insulated types need an insulator pad under them when mounting, but it's a fairly cheap way (maybe 50 cents to a dollar) to get 12V out of 24V. It wouldn't have enough "steam" to run electric brakes, but plenty to run up to 15 watts of lamps. If you tried to draw more current, the 7812 would just limit the current, and shut down - no harm, no foul.

If you can measure what current the brakes draw at 12V, I could steer you in the direction of a power resistor that would limit the current to a safe level for your controller, as long as it's the simple resistive type. If it's a newer-style electronic one, you need to use a DC-DC converter ahead of it, to feed it 12V.
 
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