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M105 Trailer wiring & build 24v to 12v 4 or 7 pin connection

mrfishaholic

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Ok, I have searched this forum through and through, and could not find clear guidance doing a search, so I am going to post what I ended up finding out.

I have an M105A2 Trailer that I purchased through gov liq. I wanted to drop the height to normal 3/4 ton truck height, and have electric brakes, (retaining 2.5 tons of cargo capacity if desired) I went with a dexter 7K axle.

I removed landing gear, pintle, and installed a manual crank jack where the landing gear used to be. I dropped all the springs and the axle, (easy as they are bolted to the frame)

For wiring, I wanted to be able to tow it with 4 pin connector or the 7 pin with electric brakes.

I ended up just wiring the 7 pin and calling it good, however, Here are the instructions for each:

4 Pin Flat connector:
Trailer Red with White stripe wire is Left Turn and brake light
Trailer Black with white stripe wire is Right Turn and brake light
Trailer Ground (common) is Black with Red Stripe
Trailer Tail Lights are Red with Black Stripe

7 Pin connector this is what I did
Red/black stripe, Tail Lights
Red/white stripe, Left Turn Signal
Black/red stripe, Ground
Black/green stripe, Electric brakes (correlates to the lowest (blackout drive)
Black/White stripe, Right Turn signal
Solid Black, 12v +
Aux I did not hook up.

You will need to replace the light bulbs with 1156 (turn, brake), 67 (tail) Turn and brake is the 2nd socket from the top or the bottom of the top compartment in the light fixture housing. Tail light is the top socket in the light fixture.

Now it only took me about 10 minutes to hook up the lights with the 4 pin flat to get it home, I just cut off the military plug and stripped back the black tubing to expose the black and red wires underneath. It took me about another 5 mins to change out the bulbs. Figuring out which was the common ground and tracing all the wires really didnt take me but 5 minutes. So hopefully this will shed some light on the reality of what the lighting 24v to 12v 4 or 7 pin connection is all about.

I will post photos of my M105A2 shortly, I need to hook up the electric brakes still, and since I am headed out on a TDY mission for a month, it will likely be the end of January before I post the rest of the story as to how to hook up the electric trailer brakes, and how I end up running the wires. I plan to use only the wires on the trailer, as the wirirng is in great shape on the trailer I purcahsed (MFG 1993).

Anyway, my trailer is the same height as my truck is now, and I love it. Perfect for hunting, camping, hauling my quad, or loading 2 cords of wood in. The electric trailer brakes were a great addition to the trailer, also allowing me to keep the weight carrying capacity of the trailer. I can load over 5K into the trailer legally, and within the weight rating for my axle, and the tires. (actually more than what the original setup was rated for). I dont have anything that heavy to load, however, If I wanted to I could do it safely. I also have a coupler at the front where I can switch between a pintle and a 2 5/16" ball. very convenient based upon on road and off road applications......
 

DUG

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How much do you think it weighs after you made all the changes? The 105 is a heavy trailer (about 2700 lbs) so with only a 7K axle I don't know if you can get "over" 5K in it.
 
Last edited:

Warthog

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Here is the military standard for numbering of the wires. This is a M101 diagram but the M105 is the same.
 

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Recovry4x4

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Just as easily you could have unplugged the military pigtail from right under the front of the trailer and added your 4 Flat using just bullet connectors. No wire hacking and you would be left with the pigtail for future use or to offset costs by selling it, lots of folks need them! Pics should be interesting.
 

mrfishaholic

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pulled her across the scale she weighs in at 1550lbs now. Those other wheels, tires, axle and springs are friggin' heavy.

I am going to take her to a certified scale later to verify. I used the local refuse (the dump) station for the weight.

I can tell you though that I can move her by myself now, lift steer push and pull on level grass, of which I could not do before my swap.

Like I said, I will get a certified weight on her, but I am confident she is less than 2000lbs.
 

DUG

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pulled her across the scale she weighs in at 1550lbs now. Those other wheels, tires, axle and springs are friggin' heavy.

I am going to take her to a certified scale later to verify. I used the local refuse (the dump) station for the weight.

I can tell you though that I can move her by myself now, lift steer push and pull on level grass, of which I could not do before my swap.

Like I said, I will get a certified weight on her, but I am confident she is less than 2000lbs.
Wow! That is a weight loss. I've changed out axles, landing gear and wheels before and I knew the stuff was heavy, just did not realize it added up to that much.
 

Unforgiven

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How much do you think it weighs after you made all the changes? The 105 is a heavy trailer (about 2700 lbs) so with only a 7K axle I don't know if you can get "over" 5K in it.

The M105's are only rated for 1.5 tons of cargo. 5K of cargo would be overloading by 66%.
 

Unforgiven

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Explain that one to the DMV. Those springs are rated at 1.5 tons. He can register it as a custom trailer build, but not as an M105 if he's going to go over 3K of cargo.
 

m16ty

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A stock M105 is way underrated on what it can haul. I had over 4K in mine and the overload sprigs weren't even touching yet.
 

steelandcanvas

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Explain that one to the DMV. Those springs are rated at 1.5 tons. He can register it as a custom trailer build, but not as an M105 if he's going to go over 3K of cargo.
I think technically with all the modifications, it's not an M105 anymore. I can see the gentleman registering the trailer custom/homemade, as you suggest. If I read his post correctly, he removed the springs anyway, most likely to drop the height to track better behind his 3/4 ton pickup.
 

DUG

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The M105's are only rated for 1.5 tons of cargo. 5K of cargo would be overloading by 66%.
Not my issue. I was doing simple math - 2700 pound trailer and "over 5000" pounds on a 7000 pound axle. The OP has since posted that the trailer weighs far less than 2700 than it originally did.
 

m35a2pat

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what size wrench did you have to use to take the pintle loop off the trailer? im assuming it was around a 2.5 but was just wondering before i start on mine.
 

armysurpguy

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New here. Forgive me if this has been discussed before.. I'm looking at buying a M105 and the seller doesn't have the title, hes just offering a bill of sale. What do i need to do to get a title made so i can register it for road use?
 

juanprado

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New here. Forgive me if this has been discussed before.. I'm looking at buying a M105 and the seller doesn't have the title, hes just offering a bill of sale. What do i need to do to get a title made so i can register it for road use?
I use Maine Trailer Registrations as it does not require a titile. Can all be done via email with a credit card and a legal registration/plate arrives in 7 days. You can always try to register home made etc but i do not know NC laws. Maine is the fast and simple route to take. Search the threads here as there are other threads on using these fine folks and Maine is a haven for trailer and over the road fleets.
 

1Marshal

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Hey just wanted to offer some info on wiring a cargo trailer for the humvee going from 12 military connection to 7 pin civilian set up. My trailer is 2006 model. This is what I discovered with the wiring color bands and others that was not used.


Solid Red-ground
Black w/green strips-running lights
Solid Black-left turn and brake
Red w/white strips-right turn and brake

Other wires (4) are not used and can be cut short in the harness.
I hope this helps someone.
 

Mike of Bonsall

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Many references to wire numbers but I want to relate choses numbers to COLOR. I cut off the 12 pin and want to know which four colors do I take to my 7-flat plug. The colors I have are White, White with stripe, Red Dark, Red Light,Gree, Blue, Orange and Black. I can work this out by trial but with so many diagrams referencing numbers i don't see why no-one has ever posted the colors.
ALSO will the 24v bulbs work but shine dimly? I have not been able to find a source for 12v equivalents.
Thanks new to trying to get this heavy M105A2 on the road in California.
 
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