Civy truck to MIL trailer wiring info

Mainsail

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Day 32 of my cold/flu and felt human enough to get some work done. The pics explain what I did. Connections other than ground are soldered and heat-shrinked inside the box. The grounds got soldered eye connectors and a screw post inside the box in case I ever need to add a ground for something. I should have gotten a bigger box. My original plan included a cigar lighter socket powered from the +12v trailer wire, but there wasn't enough room in the little box.

I mounted it temporarily on the tongue with zip-ties; I still need to seal it up with RTV. Not sure how I'll mount it exactly but it won't be permanently mounted in case I need to loan it out for a recovery. Plugged it into my jeep and everything works as it's supposed to. The bulbs were brighter than I was expecting since I haven't swapped the 24v ones out yet.
 

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Traveltocamp

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Howdy,
Most just simple replace the type they have. If you have incandescent, then you use incandescent bulbs.

PU-798A Unit = Mep-803a on a LTT-TQG trailer (M1102)
All the bulbs are standard incandescent. So swap out the bulbs for the 12v counterparts for a brighter safer day.

Rear brake, turn light bulbs #1683 24v bulbs swamped to #1156 12v bulbs
Marker lights all round #1251 24v bulbs swapped to #97 12v bulbs
Trailer plug =cut off mil end, cheap 7-way plug attached.

I am now all at a 12 volt lighting. Yes, brighter and safer.



total noob here

would I need 2 pair of each 12v bulb type?

4 1156’s

4 97’s ?


edit**** never mind lol
 
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namedpipes

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That is correct, however, the lights have been going haywire and I wonder if it’s because of the voltage.
Depending on what you mean by haywire, more likely the wiring.

A bad ground, a short, a break or a crossed wire will give suboptimal results ;) The harness is simple enough. Also, zip tying on a generic harness from Hazard Freight will give you a cheap, temporary solution if you need the trailer NOW.

Don't get me wrong, putting in proper 12v bulbs is better, but the 24's will work.
 

Traveltocamp

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Depending on what you mean by haywire, more likely the wiring.

A bad ground, a short, a break or a crossed wire will give suboptimal results ;) The harness is simple enough. Also, zip tying on a generic harness from Hazard Freight will give you a cheap, temporary solution if you need the trailer NOW.

Don't get me wrong, putting in proper 12v bulbs is better, but the 24's will work.
i wish I could post video to easier explain lol.

While using 24v bulbs with 12v power, the bulbs would only properly work(left/right/brake/hazards/running with my truck running.
I have now changed out to 12v bulbs and it seems to have fix that issue but I will be keeping an eye on it.
 

namedpipes

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i wish I could post video to easier explain lol.

While using 24v bulbs with 12v power, the bulbs would only properly work(left/right/brake/hazards/running with my truck running.
I have now changed out to 12v bulbs and it seems to have fix that issue but I will be keeping an eye on it.
To me it sounds like a grounding issue or maybe a connection with corrosion / high resistance. When the engine is running there's enough voltage to "force" the issue. The issue could be in the trailer OR the truck.
 

Traveltocamp

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To me it sounds like a grounding issue or maybe a connection with corrosion / high resistance. When the engine is running there's enough voltage to "force" the issue. The issue could be in the trailer OR the truck.
That’s what I’m thinking. The truck is new(2016)....my guess is the trailer.
 

mciikurzroot

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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
Thank you so much emmado22, while it's dark now, i will get back out early in the morning with my 12 volt source and tools and get busy finishing sorting this out, and yes for the sake of expediency i did just get conventiential 12v bulbs but will move to LED style next effort as i have 3 more of these as well [trailers] .. and i will post the trailer style number later today after i get back outside..
best: mac/mc
 
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