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Trailer Wiring Junction Box

Trailer Wiring Junction Box

Item # 38656
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Spectro Accessories and Parts - 38656
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This Spectro trailer wiring junction box provides a fast, easy way to connect the wires from the trailer connector to the wiring for either a 6-way or 7-way connector. Makes replacing your trailer's connector simple. 1-800-940-8924 to order Spectro accessories and parts part number 38656 or order online at Free expert support on all Spectro products. Great prices and Fastest Shipping for Trailer Wiring Junction Box. Accessories and Parts reviews from real customers.
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Spectro Accessories and Parts - 38656

  • Trailer Wiring
  • Junction Box
  • Spectro

This Spectro trailer wiring junction box provides a fast, easy way to connect the wires from the trailer connector to the wiring for either a 6-way or 7-way connector. Makes replacing your trailer's connector simple.


  • 7-Terminal junction box lets you easily connect your trailer wiring to a 6-way or 7-way trailer connector (sold separately)
  • Weatherproof, heavy-duty plastic protects wires and terminals from the elements
  • Mounting hardware included
  • Ring terminals (44-5310A) sold separately


  • Box dimensions with lid: 7" long x 3-1/4" wide x 2-3/4" tall
    • Overall length (with mounting flanges): 8"
  • Distance between mounting holes (on center): 7-3/8"
  • Mounting flange dimensions: 3/4" wide x 1/4" thick
  • Outer diameter of terminals: 3/16"

9709 Spectro Trailer Wiring Junction Box

Video of Trailer Wiring Junction Box

Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.

Video Transcript for Spectro Trailer Wiring Junction Box Installation

Today were going to install part number 38656. This is a trailer wiring junction box. First thing were going to do is find the location for our junction box. Were going to go ahead and install on the inside edge of the tongue. Well go ahead and hold it up to the tongue and then well go ahead and use a drill to mark it for our holes. We have our holes marked, well go ahead and remove the box, and then go ahead and drill out our hole.

Now well go ahead install our hardware and install our box. Now were going to use a quarter inch hardware to install the box to the frame. This hardware does not come with the box. With our box installed, we can go ahead and start getting our wiring ready. Well go ahead and cut our wires to the length of what we need and then well take our excessive length from our gray cable and use the white wire for our ground lead.

Were going to take the white wire, well add a couple of ring terminals, and well go ahead and connect it to the post labeled white and ground. Well also change out one of solid grommets for a hollow ground. With our new grommet installed, well go ahead and fish our wire through, and attach it to the box, and then were going to use a self-tapping screw to attach it to the frame. Now well go ahead and get the rest of our break cable ready, the gray cable will be for our electric brakes. Well cut back the gray sheath to expose our two wires.

Our white wire will go to ground, our black wire well go ahead and post to label blue, blue is only the function for brakes. Well go ahead add some ring terminals to it, then temporally put them into position. Now well go ahead and hook up our wires for our trailer lighting, well also go ahead and run it through the grommet and then go ahead and install our ring terminals. Now the brown wire on our trailer will be even running light circuit that will go to the post labeled brown, it will also say taillights on there. The green wire will be our right turn signal, well go ahead and connect that wire to a post labeled green, and it will say right turn.

The yellow wire well be our left turn signal and that will be connected to post labeled yellow and left turn. Now these wires have been loosely installed. Next well go ahead and wire our trailer connector, this is going to be a seven molded trailer wire connector, eight foot long, part number h20046. You see the seven pole and we have our wires. Once thing to know about this is that the functions do not match the colors better on the trailer. Now on the other side of the box well go ahead and replace them with solid grommets with a hollow grommet and well go ahead and run that over our wire that we can go ahead and push the wire back into the box. Then well go ahead and add our ring terminals to our wires. Now well go ahead and start attaching our wires, well start off with the green wire from the seven-pole which will be our running lights; this will be connected to the post with the brown wire from the trailer lights. The brown wire will be our right turn so that it will be connected to the post with the green wire from the trailer lights. The red wire will be the left turn function on the seven-pole, so well connect that to the post with the yellow wire from the trailer lights. Our blue wire will be our brake control power, so well hook that up to the post labeled blue. Now our yellow wire is usually reserved for reverse light or whatever function youd like. However, this application is not being used, so well just ignore that wire. Our black wire will be our 12 volt power supply, however this trailer is not using it right now, but well keep it to the junction box for our upgrade in the future. Well now go ahead and take our white wire push it to the ground from our towing vehicle that will be transferred to the trailer and well connect that back up to the white post, well get two white wires. With all of the wires in place well go ahead and tighten down the nuts. Next well go ahead and install the clamp from the wires that come in from the trailer side. Looking at the box on the left hand side there is provision for a clamp. Well make sure everything is pushed together properly and wont get pinched, well go ahead and install the cover. Well fasten and replace of these two bolts. Thats what it takes to install our junction box. All right with that it will finish it for our install of part number 38656, a trailer line junction box on this new trailer.

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Customer Reviews

Trailer Wiring Junction Box - 38656

Average Customer Rating:  4.8 out of 5 stars   (777 Customer Reviews)

This Spectro trailer wiring junction box provides a fast, easy way to connect the wires from the trailer connector to the wiring for either a 6-way or 7-way connector. Makes replacing your trailer's connector simple.


I mounted mine onto a piece of aluminum flat stock on the trailer “A” frame to reduce rock impact from Nevada’s gravel back roads. There really wasn’t good location on inside of trailer frame rails, was adding electric brakes and converting from 4 pin to seven. . I’m pretty darn happy with this junction box as it made rewiring rather straight forward. Our local 12 volt guru at the auto electric shop was duly impressed-wanted to know where I found it.


This box was used as part of an electric brake conversion on my trailer. This box was an excellent means of connecting the existing wiring and the new brake wiring into the new 7 way trailer connector. It has the required breakouts and grommets needed to make the wiring task the easiest part of the conversion.

Etrailer Expert

Mike L.


For a neat install and ease of replacement later if necessary, theres no better way to go than a junction box.



Im very satisfied with this connection box. It keeps all of the connections well insulated and out of the weather.


I like the junction box it makes it easy to wire up your trailer hook up wires in a dry secure place!


I just opened up my new Class 5 Curt XD hitch and have not yet installed it so my comments are based on first impressions only. It is very heavy duty - and heavy at 40 lbs. - made of extremely thick metal and outfitted with quality Grade 8 bolts with square necks so they won’t turn when torquing on the nuts to attach the main tube to the side mounting plates. My bolts are plated yellow (which I like) rather than silver as you may have seen in some online photographs. It is substantially beefier than my existing Grade 4 hitch and superior in every way. It’s an impressive piece of hardware. I cannot imagine anyone being disappointed with it on specifications, quality, strength, and general appearance. It’s a beast. What I AM disappointed in is Curt’s packaging and the condition in which the hitch arrived. (This is NOT a reflection on as the hitch arrived in Curt’s original packaging.) The unassembled main tube and the two side mounting plates come bundled together with nothing separating them but shrink wrap. No cardboard, plastic, even paper coming between the metal surfaces - just shrinkwrap probably not even a couple of mils thick. With basically metal-to-metal contact in an oversized-box with the bundle jostling around, it would be a miracle if there were no scratches, gouges, or some type of damage to at least one piece, which is exactly what happened to my hitch. The main hitch tube, on the exterior facing plane, on the driver side where I’ll see it every day, has some gouges on it that go through the powder-coating to bare metal. I can - and will - paint them to prevent rust (and, therefore, have to paint the whole hitch to match). But the gouges will still be noticeable as they go through the thicker, pebbly, powder-coat finish and will undoubtedly still appear as depressions in the surface even once painted. I fully realize this kind of surface damage will almost certainly happen with regular usage of the hitch anyway and that it’s certifiable to demand absolute perfection in anything. But if you are someone who cares about the aesthetics of your equipment and keeping it looking new for as long as possible, it is very disappointing to receive such an expensive and prominent piece of hardware damaged right out of the box and requiring immediate repainting. The plastic parts bag had also ripped open in transit, with nuts, bolts, shims, etc. rattling around in the box. I am dumbfounded that Curt packages such a high-quality piece of equipment so shoddily where such damage is virtually unavoidable. I bought from Curt solely due to their being an American manufacturer and to support American workers so this is doubly discouraging. It’s a trivial complaint in the big scheme of things and not worth demanding a replacement over. Just be aware that unless Curt changes their packaging practices it is very possible you will have the wind taken out of your towing project sails just as I have. Again, this in no way reflects on etrailer. My experience to date with etrailer (website, educational resources, staff reviews, ordering, tracking, email contact, etc.) has been beyond exemplary in every way. They rank as a Top Five online retailer in my opinion, maybe even the best.


I needed a way to reorganize wiring for my very old utility trailer. This wiring junction box from etrailer met my needs exactly and made my re-wiring project easy

Dale P.


It works well to organize wiring.


perfect to make a universal trailer hook-up, Hi quality parts, see adjacent review for completed assy


Installed in about 30 minutes, made install a breeze and took the mess out of a rats nest of wiring spliced under the trailer. Comes with plenty of grommets and all hardware to put together. You need to supply the bolts or screws to mount this to your trailer. Each terminal is labeled for what connects to it taking the guess work out of matching wires up.

Richard P.


Still works great, no issues at all.


Rewired my trailer and used this junction box to go from my main cable to all the individual lights and brakes. It worked great, the only thing I didn't like about it was that it only had two cable clamps on the inside

Chris B.


I still have all the electric supplies from etrailer on my cargo trailer. I have had no issues with any of your products whatsoever. I hope this helps


I purchased this product after researching current trailer rewiring methods. I recently had my entire 18' trailer wired and upgraded. The trailer is 8 years old and I wanted to replace the original 4 way trailer harness which the trailer manufacture had surrounded in electrical tape which also needed an adapter. After some research, I opted for this 7 way pigtail (50-67-005) which is the connector I needed my trucks and this junction box. (all contacts were current)
The junction box is sturdy and well made, we installed 7 way wire within the box with a snug fit. The trailer now has a clean professional appearance and most test functions can be performed from the junction box location. The junction box was installed behind the trailer tongue frame to minimize the weather elements. This product appears to seal well as the product description indicates. I am very satisfied with this product and Etrailer's customer service.


I had to swap the trailer wire connecter with a new one and didn't realize the junction box terminals were corroded and half of them twisted the stud off while removing the old wires. Found this junction box and it turns out it's an exact match. This will make mounting so much easier since the mount holes are perfectly aligned.


We wanted both a 7-wire and a 4-wire plug on the same trailer. This junction box made the installation very easy. If your connecting the Hopkins 7-wire harness to this box, you'll probably have to ignore the wire colors names and just use the location (R Turn, etc.). Both are marked on each terminal.

There are 5 different openings to choose from to route the wiring to this box and it comes with both rubber grommets to run wiring through and rubber plugs for the openings not used. A downside is that only the side with 2 openings has wire hold downs on the inside. It would have been nice if at least the opening on the opposite end also had such a feature.

It's fairly water tight and installed easily onto the frame, under the trailer. Because it's lightweight plastic, I'm not so sure how long it'd last in the direct sunlight if it was mounted on the tongue or other exterior location.


Exactly what I needed!!!


I love these boxes. I've repaired numerous trailers my sons and I own, including cargos, flat beds and horse trailers. I really like the grommet locations, cable clamping and posts for wire connections. There is plenty of room inside to neatly route wires.


Installed as I had planned and it went well. Wired the supply line to the box to all of the correct wiring terminals as it is labeled in the box. I was prepared by other reviews, things may not match up, which they didn't, but no biggie. Once I flipped a few wires around things worked nicely.


Had some real issues with this one. Should have noticed when purchasing this harnes is not wired using standard truck/trailer color format. Other than that it went together fairly nice. If the connector would come apart I was thinking of fixing the wiring my self.


Junction box was great had it installed and wires hooked up in a little over an hour. Service and shipment was better than expected. Will definitely use etrailer for more of my needs, very good company. The only thing that took a while was the molded seven connector wire colors don't all follow standards, but a test light and a few minutes and it was figured out.


Now I have a chuckwagon that is all tricked out for side marker lights and more. This box really did the trick for keeping wires organized.


I like this product. I made organizing the transition between 7 pin hook up cable and the trailer wiring much better. The previous conglomeration of wire nuts stuffed into the battery box was just a mess to troubleshoot.


I am very happy with this heavy duty J-box. The smaller one I was trying to use didn't have adequate space or heavy enough terminals for the size wire needed for the brakes on my trailer. Leave it to etrailer, they always come through for me and are an absolute pleasure to deal with, especially Danielle!!!

James H.


Love it, works great.


Thanks for your help with parts for my trailer build. My wife and I are still making custom cabinets out of curly maple. We hope to finish this winter. We have taken it out 7 times this season. Thanks again.


This trailer was built from scratch using only the metal frame. I purchased some items from etrailer an was very satisfied with the products.

Mike D.


Great job! Looks like a high quality build.

Wayne M.


Its still working great.


It was nice for organizing the wires and install. The rubber wire hole plugs are not the best. One month outside in the sun and the top one dried out and cracked. I guess install it some where it is protected from the weather.


It is going to serve the intended purpose of gathering all these wires into a controlled location. The only drawback is the labelling on the box for the wire locations is extremely difficult to read. Not a big deal.


This junction box was exactly what I needed. Had a short from cable wear and needed to splice on a new pigtail. This box made it super easy and really clean.


The product was easy to install, the wiring and connections were good to makeup

Show More Reviews

See what our Experts say about this Spectro Accessories and Parts

  • Can a Trailer Wiring Junction Box Be Used on a Trailer with a Battery and Power Inverter
    The junction box part # 38656 is a great way to organize trailer wiring on a trailer. There's no reason you couldn't use this with what you are trying to do. You would have to run the 12 volt accessory circuit of your trailer's connector to the junction box and then from there to the battery of the trailer.
    view full answer...
  • Purpose of Trailer Junction Box
    The # 38656 Junction Box won't take the place of a trailer mounted battery, but it provides a protected and organized method of connecting the wires from the trailer connector pigtail to all the various lighting, power and brake circuits on the trailer. If you watch the linked video, you can see exactly how they're used.
    view full answer...
  • Can the Trailer Wiring Junction Box # 38656 be Used with a 4-Way
    You could use the Trailer Wiring Junction Box # 38656 on a trailer with 4-way wiring. You would just have a few extra pins available on the box that you wouldn't end up using.
    view full answer...
  • Junction Box Recommendation for Camper Trailer
    Sounds like you are looking for a junction box for your trailer. For that we have the part # 38656 which would work well for you. I attached an install video for this for you to check out as well.
    view full answer...
  • Could Breakaway Battery on Trailer Power A-Frame Trailer Jack
    A breakaway battery won't have the amperage to power an electric jack most likely and even if it could you really need to keep the breakaway battery fully charged at all times so that in emergency situation when needed it will be able to do it's job. You'd want to have a deep cell battery installed on your trailer or possibly power the jack from 12 power source from 7-way trailer connector.
    view full answer...
  • Wiring Diagram for Trailer Wiring 6-Way
    Assuming your 6-way was wired up using industry standard trailer wire colors you should use the chart I attached that shows how to wire up the 6-way. Use the orientation of the screw on the center pin to know which direction is "up" and down on the diagram.
    view full answer...
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  • How Do the Wires Connect to the Pollak 11609-EP / Junction Box and Is It Water Proof
    The connections on this Trailer Wiring Junction Box, part # 38656, are made on the inside of this junction box with ring terminals. The wires will travel through the rubber grommets to enter and exit the box. This box is weather proof, but not water proof, and what that means is that it will keep rain out under normal circumstances, but if it were to be submerged the box would not be dry on the inside. My contact at Pollak said that you could probably apply a rubber sealant to the lid...
    view full answer...
  • Distance Between Mounting Holes on the Junction Box part # 38656
    The mounting holes of the Junction box part # 38656 that you referenced are 7-3/8 inches apart and are 1/4 inch in diameter.
    view full answer...
    Image 1 for
  • Troubleshooting Trailer Brakes that are Always Engaged
    First of all did this problem just start happening? If the trailer has always worked fine before on the same truck then it's likely a short on the trailer's brake wiring. I would start by cleaning the connector and make sure it's free of any debris or corrosion. Also make sure the breakaway pin is inserted properly. However, it the probem is from the breakaway switch the brakes will only be locked until the breakaway battery dies. If both of these are fine then you need to inspect...
    view full answer...
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  • What Pin Does Brake Output Circuit of Trailer Attach to On Junction Box 38656
    The terminal labeled "stop" is the correct one to connect the brake output circuit of your trailer wiring to. This would be the one fourth from the left. I attached a picture that shows all of the terminal labelled for you to check out as well.
    view full answer...
  • Testing Trailer Lights and Electric Brakes without Connecting Trailer to a Vehicle
    If you have a separate car/truck battery you could apply power to each of the pins on the trailer connector (or the wires directly some point behind the connector) and that should power on whatever is associated with a given pin.
    view full answer...
  • What is the Inside Diameter of the Grommets Included with the Spectro Junction Box # 38656
    The grommets included with the Spectro Junction Box, # 38656, have an inner diameter of .603 inches. These grommets would definitely be too small for your larger output cable and would be a tight fit with your input cable. I checked our other junction boxes and they each use grommets with the same inside diameter. These junction boxes were designed to work with coated 7-wire trailer wiring which has a diameter of .59 inches. You could possibly trim the grommets. They are .20 inches thick,...
    view full answer...
  • What Circuit of a Trailer 6-Way Should a Battery Maintainer Get Power From
    Yes, the battery maintainer you have requires a 12 volt power source coming straight from the battery and the center pin of your 6-way is exactly that so it would work very well for you.
    view full answer...
    Image 1 for
  • Is the Tow Ready Vehicle to Vehicle Taillight Converter # 118158 Waterproof
    Trailer wiring harnesses such as the Tow Ready Vehicle to Vehicle Taillight Converter # 118158 and similar units are not waterproof and so are intended for installation in some type of protected environment. Often this is behind a tail light assembly on the tow vehicle. If your application requires installation in an exposed area you will need to find a method to protect the harness from moisture and other potential hazards such as road debris. One item that may help you is a wiring junction...
    view full answer...
  • Should an Electric Trailer Jack Run Off of a Trailer Breakaway Battery
    The trailer jack should very much NOT be powered by the breakaway battery. That was likely done by the previous owner for convenience. The breakaway battery is a dedicated battery for the breakaway system only. It needs to be able to apply the trailer brakes on full for 15 minutes. If the jack was to run down the battery then the breakaway system would not be able to power the brakes for long enough. Also, a breakaway battery is too small for the power needs of a jack. Most breakaway...
    view full answer...
    Image 1 for
  • Metal Used in Terminals of Spectro Wire and Cable # 38656 Junction Box
    According to Spectro Wire, the terminals and hardware of their # 38656 junction box are chrome plated steel. The junction box actually does a pretty good job of keeping the weather out, and taking a couple of precautions like placing a dab of # 38656 dielectric grease on each terminal and using some silicone caulk around the wires entering the box would further help to exclude water. If you click the provided links, you can see an install and a product description video.
    view full answer...
  • Recommended Wiring Junction Box For Utility Trailer
    If you are wanting to secure the wiring on your trailer and keep it secure I recommend using a wiring junction box like part # 38656 on your trailer. You can place the junction box on the tongue of your trailer and run the wires from the trailer into one side of the box and on to the terminals. Then attach the trailer connector with wires cut to the appropriate length to the matching wires on the terminals inside the box and extend it so you can attach it to your vehicle. You want...
    view full answer...
  • is there Space in Hopkins Breakaway Kit Battery Box for Additional Trailer Wiring
    With the battery inside the box for breakaway kit # 20099 there is very little space for anything else. I do recommend using a separate junction box such as # 38656 which will also make installing wiring and troubleshooting easier since there will be more space.
    view full answer...
  • Comparing Trailer Wiring Junction Box 3375601100 and Trailer Wiring Junction Box 38656
    The Trailer Wiring Junction Box part # 3375601100 and Trailer Wiring Junction Box part # 38656 are both pretty standard 7-terminal junction boxes. The latter is slightly smaller so there will be more places to mount it so that is what I recommend but you really can't go wrong with either option.
    view full answer...
  • How to Get Seperate Wiring on a Trailer From a Tow Vehicle with Combined Wiring
    What you're going to need is part # 118158. To convert from combined wiring on your tow vehicle to seperate wiring on your trailer you will install the # 118158 on your trailer's wiring between the trailer connector and the lights. Connect the wires as such: From trailer connector to Input side: Right Turn to green wire Ground to white wire. Left Turn to yellow wire Output side to lights: Green wire to right turn signals Red wire to both brake lights Yellow wire to left turn signals The...
    view full answer...
  • Can a 7-Way Junction Box Be Used for a 4-Way
    There's no reason you couldn't use a 7-way junction box like the part # 38656 to install a 4-way. It would be just a matter of wiring up only 4 posts of the junction box on the input and output side of the box instead of 4. With only 4-wires going into and out of the box the rubber grommet would be too big to provide a seal for the wires. You would need to use a sealant like # 0160297 to seal the grommet. I attached an install video for you to check out as well.
    view full answer...
  • Is there a Replacement Junction Box for a 1997 Dutchman Aristocrat
    We have numerous junction boxes but if you are talking about the transfer switch/fuse panel then we do not have those types of parts and you would need to speak with the trailer manufacturer for a recommendation. If it is just a regular junction box such as # 38656 then we do have those. I have included a link to them below for you.
    view full answer...
  • Electric Trailer Brakes Lock Up While Connected to Tow Vehicle
    There appears to be a short between the brake output wire and the 12 volt power wire either on your trailer or tow vehicle. This is why the issue is only occuring while connected to the tow vehicle. Unfortunately, the brake output wire goes from the brake controller in the vehicle all the way back to each braking assembly and the 12 volt power wire goes from the fuse box all the way back to the trailer battery. The short could be anywhere on these two wires so I don't have an exact place...
    view full answer...
  • What Are The Dimensions Of The Trailer Wiring Junction Box
    The dimensions of the trailer wiring junction box, product # 38656 are, length 7 inches, width 3-1/2 inches, height 2-1/4 inches and the mounting flange distance is 7-3/8 inches on center and is 8 inches overall. Mounting flanges are 1/4 inch thick plastic.
    view full answer...

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