Seeking advice/specs on first DCC install


I’m embarking on my first Dcc installation as part of my sw1500 ktibash project. I’ve read lots and lots of posts here and elsewhere about decoder, light, and speaker installations. I’ve got several questions as a result, and I’m hoping I can get them answered before the glue and solder and drilling gets too far along.

The context is: an sw1500 kitbashed from an Atlas mp15dc, with the drive utilizing the gearboxes and motor from an Atlas sw8/9/1200 chassis. It’s a drop-in fit as the truck and motor mounts are the same for both types of Atlas switchers, and the sw1500 and sw8/9 share the same bolster spacing. So I would presume that motor amp draw and performance would be familiar to those here.

I’ll start with some pictures to show how I’ve got things arranged.

Decoder is a Loksound L Select. Speaker is Tang Band 1931 - yup that’s right. Tabs removed, material removed from both sides of the speaker, plus from the engineer’s side of the shell (accounting for the hand brake recess on the left side). I’ll post about this on the Tang Band thread. But it fits, and I didn’t breach the speaker enclosure. Life would be much simpler if I went with the 1925 module here, but no guts no glory as they say. I hope the 1931 sounds awesome.

Intended lighting includes numberboard over the cab, front and rear headlights, and left and right ground lights under the cab. Ditch lights are a remote possibility, but I haven’t nailed down an era yet for this model, so I may or may not need them. The switchers do not appear to have walkway lights at the bottom of the hood ends, and most of the SP units that I’m considering do not appear to have step lights either. I do know that the era I will be modeling will be post removal of gyralights and blanking of class lights, so I don’t need those, and I don’t need cab lights or gauge lighting either. I suppose the full SP light package would be cool, but it doesn’t really do much for me, so I’ll pass on that opportunity.

The decoder and speaker will sit on a styrene shelf. The shelf will have a “beam” running the length of each side, plus blocking, to prevent sag. The beam is .125" x .250" Evergreen tubing, so I can use if as a conduit to route wires through to avoid entanglement with the flywheels or any other moving parts. There will be an additional pair of styrene tubes under the shelf for conduit, as room allows.

I think that should describe the arrangements well enough. On to the questions.

What wire gauges should I use? I have the impression I might use three different sizes for track power and motor leads (24 gauge?) , speaker (30?), and lights (magnet wire?), all stranded. Can I just use something like a Digitrax harness, which I think is all 30 gauge, or do I need to use something different.

Should any of the wires be twisted, is it required anywhere, or is it something that should be avoided.

I see where Bob used what I presume are nylon screws to mount the decoder motherboard. Is this required if mounting to styrene? I presume this is for electrical isolation.

The Loksound motherboard appears to have the solder pads already primed with solder on the bottom side of the board. In a picture in one of the trheads here, it looked to me like Bob had soldered to the pads on the top side of the board instead. Is there a preference? Does it matter which side is used?

At a minimum, I would like to have the headlight leads connected with plugs or screw terminals, located underneath the exhaust manifold hood piece, between the decoder and speaker. And possibly the leads from the trucks as well. However, I don’t have a lot of space left between the decoder and speaker. So I would be interested in the smallest plug or terminal block, that would be reasonable to use. I can gain some space underneath the decoder if I elevate it from the shelf with some spacers, so that’s a possibility. But I can’t move the speaker forward as I need clearance for the radiator fan enclosure, and it would cover the screw positions where the board will be attached to the two existing lugs on the frame. I can’t move the decoder back as it is essentially up against the position of the cab wall now.

Lastly, I could use some suggestions on led and resistor specs for the lighting. I’m planning on reusing the existing Atlas numberboard light tube, in cut down fashion, for the headlights. I will be fabricating or printing a new numberboard housing for over the cab, and I will probably attempt something similar to Bob’s numberboard and ground light installations on his gp9. What I’m not sure about is which led’s to use. I see reference to something like “0603” led’s. Is this a size specification? Is there a color temperature which is best? Do all led’s require a resistor? Should I stick to Cree products?

Any specific information, suggestions, tips, admonishments, or other commentary would be greatly appreciated. As noted, I’ve done a lot of reading already, but often I find content that is based on HO rather than O scale installations. I’ve also spent a lot of time getting lost on the Digikey and Mouser websites. Those can be a bit overwhelming if you’re not sure what you are looking for already :open_mouth::thinking::astonished:.



Wow, Jim. That’s going to be 10 pounds crammed into a 5 pound bag!

I’m not enough of a masochist to try to fit a 1931 module in one of my Atlas SWs! :exploding_head: I like having extra room inside to neatly dress wires in place, and for an ESU PowerPack. I hate it when a wire gets pinched between the shell and chassis during assembly. If not noticed in time, insulation could be pierced and bad things could happen. :roll_eyes:

Curiously, a 1931 fits width-wise in an Atlas metal SW8/9 shell. But vertically it might be too tight. The speaker cone needs adequate clearance so when it moves it won’t hit the radiator. Your 1500 has less taper in front of the cab than an SW 9 so there is a bit more width and height for the install.

That said, I could lower the styrene platform in my SWs by just a few mm before the styrene hits the motor. A 1925 module would be a pretty easy fit. I presume you’ve checked clearance above the motor to the styrene platform on the MP15 chassis.

And don’t forget about the volume under the motor in the fuel tank! There’s a generous volume on the SW8/9, enough for a small PowerPack or, if I mill the inside a bit, a large PowerPack.

As for wire gauge, the only wires that need to be a bit heavier go to the motor and wheel wipers. These wires are short so resistance won’t be an issue. 26 gauge stranded should be more than adequate. Smaller than 26 might not be mechanically durable when flexed by truck motion.

Lighting and speaker wires can be any gauge. ESU sells some very nice 36 AWG stranded that is extremely flexible. Magnet wire, being solid, has a tendency to crack, especially if there is even a tiny nick from removing insulation with a knife. There is no need to twist any wires unless that makes them easier to manage, which may be the case particularly with lighting wires.

I often use nylon screws because I don’t want to be concerned about any sneak paths to the chassis from a solder pad. Alternatively double-stick tape can work nicely. I find that my local Ace Hardware sells a roll of Loctite branded tape that is clear plastic instead of foam. It is a lot easier to rework an install than with the typical foam. Just keep the foam on the daughter board, not covering the electronics on the decoder itself, which could cause it to overheat.

The solder pads on the top and bottom of the decoder daughter board are identical. Solder to whichever one(s) you like. The bottom pads are already tinned but with horrible unleaded solder. Pads on the top need to be tinned before making a connection.

Regarding LEDs, the ones I really like are discontinued! When I found out that they were going away I bought a lifetime supply. There are alternatives, and picking the “right” ones depends a lot on your preferences and skill levels. If you go browsing on Mouser, for stuff like number boards and ground lights look for ones rated at 2700K color temperature. Headlights are usually 3000K.

On a prototype switcher, headlights on both ends would normally be on dim so long as the engine was working in a yard. A&O operator Jay says that when he was employed in engine service in the Grand Junction CO yard, his switcher headlights never went to bright unless he couldn’t see which way a switch was thrown. The Atlas SW8/9 comes with incandescent bulbs. Today the best 3mm conventional “warm white” LEDs I’ve found come in 10 packs from NCE. The pack I sampled had the most uniform color and the least amount of a green ring off-axis.

For cramped spaces, it is hard to beat pre-wired “super golden white” LEDs from German eBay seller LEDBaron. Their selection varies, and they often have either 0402 (that’s 0.040" x 0.020") or 0603s with either very fine stranded Litz wire or magnet wire. Both need to be insulated with a dollop of glue such as ACC to keep them from shorting if installed in a metal fixture. I was able to give under-cab ground lights on an Overland Also C430 “root canals” with a very fine bur and a “screaming banshee hand mill.” The 0402 LEDs fit quite nicely.

Finally, where do we get plugs? Well, a lot depends on whether we planned enough space for them. I doubt that you will be able to use screw terminals in your installation because they take a LOT of room. Typically I make my own plug pairs using 0.1" snap-apart pins. These are available from many sources including Mouser and Miniatronics. One Mouser part number is 310-13-132-41-001000 for a 32 pin strip.

There are even narrower pin sets. Mouser currently sells part number 851-93-050-10-001000 from Mill-Max. These are 50-pin strips with pins only 0.050" apart. I have some samples but haven’t yet used them.

When making a connector pair using these strips, it can be helpful to make the connector 1 pin too long. Cut off the male and fill the female cup with solder. That way it becomes polarized and quite difficult to plug in backwards.

For resistors, a fairly standard choice would be a 1K ohm 1/4 watt. Mouser sells some that are quite small compared to what’s typically available. Mouser part 299-1K-RC would fill the bill quite nicely. These are only 3.5mm long plus leads and 1.85mm diameter, plus leads. Considering the price breaks, you will probably end up getting a lifetime supply of 200. Also useful might be the 2K ohm resistors for a bit less brightness.

Note that except for the headlights, you can wire pairs of LEDs in series for things like number boards and ground lights. That cuts down on the number of connector pins. Just use a single resistor in series with either lead of each pair.

Also of note is that the Loksound decoder can adjust each function output to one of 31 different brightness levels. So if a light is too bright, you can tame it using a LokProgrammer or DecoderPro.

I hope that covers your questions for now.

When you get everything buttoned up, I’m sure you will be impressed with the bass response. There’s a lot of delicious low bass in the ESU 74343 12 cylinder 645E file. :yum:


Thanks for the prompt and thorough reply. You are right that there won’t be much free air left inside the shell once everything is installed! And I too would prefer to have some room to elegantly organize my wiring. It’s that compulsive thing again. :roll_eyes: I had thought that there would be plenty of room when I mocked things up, but either the parts got bigger or I misjudged something along the way. I might have thought that I had all the way back to the rear bolster for the shelf and decoder, but that bolster is in fact under the cab floor. I can extend back toward the cab somewhat, but whatever is there must fit under the cab floor, so I can’t do much with it.

At the moment I’m thinking about sliding one end of the motherboard under the cab floor, as long as I can get the wires turned back around and heading forward cleanly. It really would be swell if the motherboard swapped a pair of speaker pads with a pair of the auxiliary pads end to end. Then a basic installation could be done accessing only two sides of the board. Food for thought.

The goal is that with the conduits, good planning, careful execution, and dumb luck, all the wire will stay pretty, free of moving parts, and unpinched. I’ve got a pretty good idea where everything will go, and now that I know that wire sizes are fairly small, I’m feeling more confident that everything will fit neatly.

Addressing other points about space, it makes sense that the 1931 would fit in the sw9 shell width wise, as the prototype shell is something like a foot wider than the later hood styles. This is also why the sw9 hood tapers inward as it approaches the cab. The later hood style is only six feet wide for the whole length, so it doesn’t taper at the cab. Regarding height, you’ve noted that the radiator core is recessed by 7" on the sw9, whereas it is flush with the hood on the sw1500. If I had the same height constraint as you do with the sw9, I’m sure I would have already settled for the 1925S.

For motor clearance, tests indicate that 1/4" beams clear the top of the motor, but 3/16" risers leave the bottom of the shelve essentially sitting on the motor. I can however add an additional .125" x .250" tube oriented horizontally on each side, tucked up against the vertical beams. These clear the motor due to the curvature of the housing. The best thing to have would be a 45/45/90 triangular piece of tubing to fill the void around the motor most efficiently.

I have never even considered attaching a keep alive board. I’m not opposed, I just never really thought about it. Unfortunately the fuel tank has been heavily modified to reduce it’s size to prototype dimensions. Most of the void is now filled with brass in the form of splice plates or the mounting bracket. In fact, the frame with revised fuel tank and new turned brass air reservoirs weighs more now than it did before modification, even with the diecast chunk removed from the tank area and two feet of frame removed. So neither a keep alive or a tweeter will fit in the fuel tank any longer. It’s something I will think about when I do a second sw1500. There’s quite a list of things I will do differently on the next one :roll_eyes::thinking:.

Lastly, I don’t anticipate any issues with cone excursion. We discussed this in the Tang Band thread. I should have enough clearance as is, but if not I can modify the rib down the underside of the radiator core frame to gain another 1/8" or so.

Now for all the DCC info, this is exactly the type of help I was looking for. I will start gathering materials this week now that I have a sense of what to look for.

I have two additional questions though. With the snap-apart pins, I had presumed these were for use with PCB applications? Can I just solder directly to the pins on these? And what do I plug into them? I only ever see photos of the empty sockets with nothing plugged in. Is there a corresponding “male” pin, or does each piece fulfill either male or female role depending on which end the wire is attached to?

The second question is about the led’s. For a light tube headlight application, I presume I would use something like the 0603 led? And that the 3mm conventional led’s would be used if the led itself was supposed to represent the headlight lamp? 3mm would be just about right for EMD twin sealed beam lamps as they measure about 6.25" across the exposed face.

Thanks again for all the information and observations. I want to keep inching along with this project. I’d like to take something to the March meet next year, so I need to keep moving.



Jim -

Think of the 0.1" and 0.050" pins as “hermaphrodites.” The pins on the bottom fit into the cups on the top. The important bit is making sure that everything is well insulated and has an adequate strain relief. When not soldered to a PC board, as between a steam tender and locomotive, I usually insulate exposed pins with fine heat shrink tubing, then slip a larger piece over the collection. Wires soldered into the cups can be harder to insulate; either heat shrink around the whole body of the connector or a squirt of silicone rubber might prove adequate.

As for headlight LEDs, on my SW I punched the clear plastic headlight and light sprue out of the SW9 fixtures. Each received a pair of 3mm LEDs. New “glass” for number boards was carefully cut to size and held in place with Kapton tape, then the interior volume just behind the glass packed with gloss medium. When dry I inserted the LEDs. That produced headlights that produce a flashlight-like beam pattern, which frankly are too bright for a switcher. When I retrofit a Loksound decoder I’ll take them down a few notches.

The brass part in the second photo is a cutting guide I milled. The perimeter of the glass needed to be painted black to prevent light leaks.

Alternatively you could leave the Atlas clear plastic insert in place and aim a 3mm LED into the back of the fixture, with or without a light tube. A light pipe could be a different story; you could either file a 3mm LED flat and glue it to the pipe or use a surface-mount part.

For sealing light leaks I prefer gray or black non-hardening modeling clay. It is opaque and easy to rework. A third option, not as bright, would be a surface-mount LED firing into the back of the clear plastic insert. I’m not sure what packing a light pipe with clay would do for light transmission. Those depend upon nearly-total internal reflections due to the difference in the index of refraction between the plastic and air.

Number boards can be tricky depending on how much room you have. I don’t know how many lamps were in SW1500s but there might have only been one given how small the boards are. On ALCOs and a lot of EMDs, there were two bulbs behind the number board mounted on the nose. I recall seeing an ex-SP 1500 outside the Cheyenne roundhouse and that one had boards on the cab. On a prototype SW8/9 fixture like the one shown there was only one light bulb inside that illuminated both boards. There’s an old thread on one way to light number boards on a C425. If you want to go this way, Mouser still carries some suitable 2700K 1206 surface mount LEDs from a different manufacturer that are fairly easy to solder. Let me know if you want a part number.



Jim -

I found a couple photos of UPY 1062 in Cheyenne. It looks like spaces behind the headlights and the number boards above the cab are extremely limited. They might call for surface mount LEDs.

And there might be a bit more room under the radiator, since it sits pretty high in the car body.



The unit you photographed in Cheyenne is essentially identical to what I am aim trying to model. My version will have a recessed area in the headlight housing where the two gyralight fixtures were removed and blanked over, as seen in this cad screen capture.

The backside of the print will have a void for the headlight arrangement. I have no idea if it will be large enough at .344" x .167". The trick will be to choose the right led’s, or the right combination of led and light tube.

Here is the light tube as it came out of the numberboard. I may be calling this a light tube when it’s only an insert. The headlight lenses have a good shape to represent the lamps in the housing. I have been thinking about trimming off the numberboards and using just the middle part for the headlights, with an led behind to light things. Based on your comments, I’m now not sure if that will work. This part will require more thought.

There is actually a decent amount of room in the cab mounted numberboard housing. It is more or less the same as the housings found on most if not all 2nd generation EMD cabs, except it is only about 15" tall. The actual numberboards are the same size as those on road units, and the housing is about the same depth. I’m not sure if I am allowed to post a photo that isn’t mine, with attribution, for reference sake. If so I have a decent shot of the numberboard from slightly above that gives a good sense of its size. At any rate, it offers more room than the headlight, but will still be a tight fit. There’s no volume of hood or cab behind it for hardware to spill into.

I don’t suppose you have any photos of the coupler pocket (front and back side) and draft gear on that sw1500? I’m trying to nail down how the coupler yoke looks coming out the back end of the pocket, and also what the alignment blocks look like on either side of the shank on the front side, if they were used. It’s possible also that the pockets and draft gear from that switcher you photographed being cut up might be applicable.



Well let me take a look. I might just have some high-resolution photos. I don’t know if they reveal what you want to see. Click on them for the bigger views. Once enlarged, you can right click on a photo and open it in a new window to see the full-resolution version.

Here’s the rear.

And one of the front.

Hopefully one of them is a money shot.



You weren’t kidding about the high resolution! Those are beautiful shots, loaded with information. I was looking for a shot of the coupler alignment keys, which are those pieces pinned to either side of the coupler pocket, wrapping around the end of the plate and disappearing back along the coupler shank. So got that one. When I said “back end” of the pocket, I meant the area behind the pilot end sheet, rather than the rear end of the locomotive. Circled in yellow below:

The coupler yoke and draft gear should extend through that notch in the rear plate of the coupler pocket. I would like to represent that on my model, even if the draft gear isn’t operational. I have plenty of data on coupler pockets for road locomotives, but the switcher assemblies are smaller and slightly different in style. So the search will continue.

There are so many missed opportunities from my time in Denver for data gathering that I missed or simply failed to take advantage of :face_with_symbols_over_mouth:. Things I didn’t yet realize I would want in the future, or events like the Depot Days that I may not have known about. Worst of all, the end cab switchers were all over UP’s North Yard while I was there, and now they are disappearing there and everywhere else, so opportunities for pictures and observation will become even more scarce :cry:.

Thanks for the pics, they will help tremendously with my model.


You’re welcome, Jim. I checked and don’t have any photos that show the area circled in your CAD drawing. But I do have a bunch of other photos, in the cab, around the trucks, traction motor cables, etc.



This is the only photo that shows any part of the area you circled. Of note are two things: the pipes visible through the stairway and the fact that both brake line hoses are mounted on the engineer’s side of the couplers.


All photos are welcome and helpful. I’d be more than happy to take any that you are willing to share. If you want to discuss offline, shoot me an email at and we can arrange something like Dropbox if there are a lot of photos. I’m happy to agree to and respect any terms of use.



Jim -

There is a new gallery on my Smugmug account with photos of this locomotive.



Thanks so much for posting all of these photos. It’s very generous of you to share. And they are pure gold for me, especially the shots of the cab interior. But I can use all of them, to either glean new information, or confirm observations and decisions already made. In the first photo, I’m even able to sneak a peek at enough of the back of the coupler pocket to see that the draft gear isn’t particularly evident protruding out the rear. I’m guessing that the yoke slides out the back end when the couplers get bunched, but retreats back inside when the draft gear is in a neutral position.

If there’s ever anything I can do to help you with something, please don’t hesitate to ask. I suspect that the only thing I can offer is 3d cad work, as it appears your level of proficiency exceeds mine in most other aspects - I’m pretty new to non-armchair modeling. Radiator parts are available if you want and can use them, and highly detailed flexicoil trucks are around if you ever decide on an sw1200rs. Sometime in the near future, I’ll have AAR type “A” sideframes drawn up as well. I can draw most anything else you might want, all I need are specifications.

Thanks again,


Hey Jim, nice build!

Bob is a pro and an artist with the sound and electronics!

I’m interested in your SW1500 project from the model side. Maybe you could start a new topic on the build so we can not contaminate this thread? Jay and I have been talking about my research into scratch building a SW1000 and your build is very interesting to us!


Hi Rick,
Thanks for the positivity!

It’s no accident that I asked for dcc help here. I’ve read most if not all of Bob’s threads here about dcc, and sound, and lights, and more lights, and, and, and…:smirk:. I knew I would get pertinent advice because I can see that we approach things with similar goals.

I had the exact same thought about starting a build thread on the loco and keeping this thread more focused on the dcc and sound install. I will get one going in the next several days, or maybe over the weekend. I need to get pictures organized. I can definitely help you with an sw1000 build, both info wise and parts wise. Let me get some stuff sorted out.