Add 7 blade /4 pin receptacle to M939

nayrbrellim

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I've searched the site here a bit and can't seem to find exactly what I'm looking for...

I recently purchased a military trailer that already has a 7 blade receptacle on it.

I know they make trailer cable to convert between the NATO 12 pin and Civilian 7 blade but they are hundreds of dollars.

Can I simply buy a 7 blade /4 pin receptacle and wiring harness similar to what I have attached and splice it into the truck wiring?
Thereby keeping the 12 pin receptacle in original configuration and just adding the 7/4 receptacle.

Thanks for any input.


 

Coug

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I believe that you can, but the 12 pin nato runs 24V, and civilian 7/4 runs 12V trailers typically, so either you'll need to change all the trailer bulbs to LED or use step down converters to bring down the voltage. It is very likely that the trailer had 12v bulbs installed when they changed the cable on it, but maybe they did multi-voltage LEDs.

There are a couple threads on here in different forums where people have made their own, mounting multiple 24/12V converters in a weatherproof box and wiring everything into the truck, at a cost of around $100, but lots of Chinese components.

This thread talks about wiring and whatnot for adapting between the two.

personally I spent the money and bought the XM381 ruggedized frame mounted converter because I tend to tow multiple different trailers with my HMMWV and didn't want to so any splicing and dicing of my wire harness. This site also has good info on the wiring in the plugs. The cheapest box costs $250, the tougher one costs almost $300, but it's what the military uses on their trucks.
 

simp5782

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Take a 12pin intervehicle cable. Cut it. Install transducers on applicable wires for lights. Add 7pin female on other end.

Transducer are cheap. They also make 4 and 6 pin step down boxes

I tapped off into mine at the tail light pig tails
 

nayrbrellim

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I believe that you can, but the 12 pin nato runs 24V, and civilian 7/4 runs 12V trailers typically, so either you'll need to change all the trailer bulbs to LED or use step down converters to bring down the voltage. It is very likely that the trailer had 12v bulbs installed when they changed the cable on it, but maybe they did multi-voltage LEDs.

There are a couple threads on here in different forums where people have made their own, mounting multiple 24/12V converters in a weatherproof box and wiring everything into the truck, at a cost of around $100, but lots of Chinese components.

This thread talks about wiring and whatnot for adapting between the two.

personally I spent the money and bought the XM381 ruggedized frame mounted converter because I tend to tow multiple different trailers with my HMMWV and didn't want to so any splicing and dicing of my wire harness. This site also has good info on the wiring in the plugs. The cheapest box costs $250, the tougher one costs almost $300, but it's what the military uses on their trucks.
The trailer does have LED bulbs and the person I bought it from used some adapter to hook it to their Deuce and half. Unfortunately on my 5 ton I only have the 12 pin. I think Im going to attempt to splice into the wiring harness on the truck that way I can haul basically any trailer (with LED bulbs at least).
 

juanprado

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Best way is to use military Y's and the oe connectors to maintain your wiring intergrity and waterproofing instead of splicing. Many vendors sell the y's and wiring tid bits that advertise here or epay...
 

nayrbrellim

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Best way is to use military Y's and the oe connectors to maintain your wiring intergrity and waterproofing instead of splicing. Many vendors sell the y's and wiring tid bits that advertise here or epay...
I am not entirely sure what these "Y's" are. I've been scrounging all over the internet and these pages - lots of good information but almost too much info.
Seems to be a simple task (I wish this was the first time I ever said that and regretted it) to just cut the wiring harness before the truck 24 pin receptacle, only cutting the 7 wires needed for 7 blade wiring harness, connect the 7 blade harness into that, elec tape it all up and rock on
 

NY Tom

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nayrbrellim

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Outstanding! Thank you all, I have have had such good input from everybody on here.

I'm going to order these right now.

Is it a crimp type of connector I guess?
 

M37M35

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Unfortunately on my 5 ton I only have the 12 pin. I think Im going to attempt to splice into the wiring harness on the truck that way I can haul basically any trailer (with LED bulbs at least).
Just be careful that you or someone else doesn't plug in a trailer that doesn't have 24v compatible bulbs or LEDs, or you'll burn out every light on the trailer! And not all LEDs can handle 24v! If they're not designed to work on 12v and 24v then they'll burn out on 24v.

...the 7 wires needed for 7 blade wiring harness...
You'll only need 4 of the 7 wires, and only 3 need to tie into the the truck wiring.
A standard 7 blade harness has:

Ground.
Left Turn.
Right Turn.
Tail/Marker Lights.
Backup Lights.
Electric Trailer Brakes.
12v Positive.

You'll only use the first 4, and the ground should be tied to the truck frame instead of the truck wiring harness. So you'll be plugging your Y connectors into the Left Turn, Right Turn, and Tail/Marker Light wires.

Your 5 ton doesn't have backup lights or electric trailer brakes, and I don't remember if there's a 24v positive in the harness.

If you want to pull any civvy trailer without having to worry about what bulbs/LEDs it has, do what was mentioned above and get three 24v to 12v converters and install them between your truck harness and new 7 blade connector on the Left Turn, Right Turn, and Tail/Marker Light wires.

 

nayrbrellim

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... And to have it all handy, and to knowing what goes where, here are the terminal numbers & designations....

View attachment 830045
Update: So I got the Female Y connectors (and of course I didn't remember to order the male Y connectors, they should be here Tuesday) But I thought I would go ahead and snip and mark the wires so then all I had to do is connect the Y connectors.

My 24 pin plug doesn't have the notch to help identify which way is up but I did have the metal crimp id tags on there with the numbers so I was able to identify which wire is which.

The question is, M and N are blank (no wires on the truck side) but on the 7 pin wiring harness they are the LH and RH turn signals? the Yellow is LH indicator and the Green is the RH indicator. Does this mean the trailer won't have turn signals on it?

Also, should B & J (LH and RH stop light) be connected to the single Red wire on the 7 pin harness?
 

nayrbrellim

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Just be careful that you or someone else doesn't plug in a trailer that doesn't have 24v compatible bulbs or LEDs, or you'll burn out every light on the trailer! And not all LEDs can handle 24v! If they're not designed to work on 12v and 24v then they'll burn out on 24v.



You'll only need 4 of the 7 wires, and only 3 need to tie into the the truck wiring.
A standard 7 blade harness has:

Ground.
Left Turn.
Right Turn.
Tail/Marker Lights.
Backup Lights.
Electric Trailer Brakes.
12v Positive.

You'll only use the first 4, and the ground should be tied to the truck frame instead of the truck wiring harness. So you'll be plugging your Y connectors into the Left Turn, Right Turn, and Tail/Marker Light wires.

Your 5 ton doesn't have backup lights or electric trailer brakes, and I don't remember if there's a 24v positive in the harness.

If you want to pull any civvy trailer without having to worry about what bulbs/LEDs it has, do what was mentioned above and get three 24v to 12v converters and install them between your truck harness and new 7 blade connector on the Left Turn, Right Turn, and Tail/Marker Light wires.


what I found for wiring the 7 pin harness:

Yellow to M LH indicator - M is blank on the 12 pin truck side?
Blue to F - good to go
White to ground - frame of truck - good to go
Green to N RH indicator - N is blank on the 12 pin truck side?
Brown to E - good to go
Red to B & J LH stop and RH stop - do I hook both B & J to the single red wire on the harness?
Black to E - no black wire on the harness?

There is also a purple wire on the harness, not sure what it ties to? more internet times makes me think the purple wire is for backup lights, which I dont have of course of the 5 ton.
 
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M37M35

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what I found for wiring the 7 pin harness:

Yellow to M LH indicator - M is blank on the 12 pin truck side?
Blue to F - good to go
White to ground - frame of truck - good to go
Green to N RH indicator - N is blank on the 12 pin truck side?
Brown to E - good to go
Red to B & J LH stop and RH stop - do I hook both B & J to the single red wire on the harness?
Black to E - no black wire on the harness?

There is also a purple wire on the harness, not sure what it ties to? more internet times makes me think the purple wire is for backup lights, which I dont have of course of the 5 ton.
Ignore the purple, blue, and red. Don't hook them to anything, just tape them up out of the way.

On your truck, use the metal wire number tags on the wires on the back of the plug.

White to the truck frame.
Green to 22-460
Yellow to 22-461
Brown to 21
 

nayrbrellim

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Ignore the purple, blue, and red. Don't hook them to anything, just tape them up out of the way.

On your truck, use the metal wire number tags on the wires on the back of the plug.

White to the truck frame.
Green to 22-460
Yellow to 22-461
Brown to 21
Yeh this is kind of what I was thinking as well.

What about the Blue wire?
I'm finding two different entries for it - fog lights or brake controller?

Thanks for the feedback by the way
 

nayrbrellim

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And the saga continues...

So come to find out the guys who powder coated the trailer unplugged all of the trailer light connectors (4 for each light). They appear to not have any markings on them or any other identifying characteristics. Any suggestions on best way to figure how to connect these back up?

I was thinking plug the trailer into the truck, turn on left turn signal and start pluggin them in, one by one but not sure if this is the best way to do it?

thanks
 

M37M35

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What about the Blue wire?
I'm finding two different entries for it - fog lights or brake controller?
Don't use it. If you already hooked it to something, unhook it and tape it up out of the way.
It's for electric trailer brakes, but a stock 5 ton doesn't have any provision for controlling electric brakes on a civilian trailer.
 

M37M35

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And the saga continues...

So come to find out the guys who powder coated the trailer unplugged all of the trailer light connectors (4 for each light). They appear to not have any markings on them or any other identifying characteristics. Any suggestions on best way to figure how to connect these back up?

I was thinking plug the trailer into the truck, turn on left turn signal and start pluggin them in, one by one but not sure if this is the best way to do it?

thanks
Are the trailer lights civilian or military?
What colors are the wires coming out of the lights?
Are there any manufactures name or numbers on them?

Post some pictures of the lights and wires, lets see what we're dealing with.

You can plug them back in one at a time and try to find the right combination, it shouldn't hurt anything.
 

nayrbrellim

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Reidsville, NC
Are the trailer lights civilian or military?
What colors are the wires coming out of the lights?
Are there any manufactures name or numbers on them?

Post some pictures of the lights and wires, lets see what we're dealing with.

You can plug them back in one at a time and try to find the right combination, it shouldn't hurt anything.
Its a military tilt trailer. Lights ar e the typ military lights, 5 plugs but only one is still plugged in. No markings at all that I can see, just 4 female packard connectors and 4 male packard connectors.

The previous owner installed a 7 blade harness so he could tow with his civvie truck. After all this I'm wondering if I should've just replaced that harness back to a 24 pin trailer receptacle, oh well - live and learn.

I think we're just going to try the ol plug this one in and see if works, then the next one etc etc.
 

nayrbrellim

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Location
Reidsville, NC
Are the trailer lights civilian or military?
What colors are the wires coming out of the lights?
Are there any manufactures name or numbers on them?

Post some pictures of the lights and wires, lets see what we're dealing with.

You can plug them back in one at a time and try to find the right combination, it shouldn't hurt anything.
Upon closer inspection yesterday, the lights on the trailer are marked white/grnd, green, yellow, blue and brown. I assume this is the same as the 7 blade harness colors: Yellow / LH turn & stop, etc. 7The 7 blade receptacle is all hooked up on the truck now ( I only used Yellow and Green wires, and ground the white to the vehicle). When I use a multimeter to test the receptacle at the truck, i get a reading when left turn signal is on from 9 oclock blade and 7 oclock blade, which is what it should be. When I use same multimeter to test the wiring at the trailer i just cant get a reading to establish which wires are which. On the right side I did a reading from to wires that indicated ground and green, but when I plugged in the tail light to it, it still didnt work.

I know you guys are the experts but I still am wondering if I need any of the other wires from the 7 blade harness connected to complete this.

I went back through this thread and realized I did NOT hook up Brown to 21 so I will do that this morning but I don't thik that will resolve my situation entirely.

Thanks again for your help guys, I about to light a match to this whole trailer thing, feel like i'm losing it.
 
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