More details, with photos ...

With knowledge at my side, I went looking around. I could purchase LEDs with wires attached and the price ranges. I have some soldering skills and thought I could do it myself. I went on eBay and found some bulk sellers of these SMDs from China. I bought way more than I could ever need with the idea I might solder up some and offer them for sale.

When they arrived I was surprised at how small (0402) the smallest was. I armed myself with a very fine soldering iron tip, some 0.1mm magnet wire and slipped on my optivisor. I was successful on my first try! Amazing amount of light that comes from that tiny spec. 

Next I wanted to apply this. I have a GE 44 Tonner project on the go which is all ready for paint. Before I could paint, I wanted to have the lighting figured out. Now there is lots of room to put even a 5mm LED in the shell and have it light both of the dual headlights. I thought what fun it would be to have an LED for each headlight, totalling 4. 

I dug took out my SMDs and decided that two of the 1206 LEDs would fit side by side. No need to use a smaller LED when this was one of my first tries.

First, I needed to determine which end of the LED was which. There is an arrow printed on the back of the LED showing which end is which. The arrow points to negative. 

I measured the distance between the headlights centre to centre with my calipers and used the tip of the calipers to put 2 dents in a piece of paper. I marked those dents with a sharp pencil. This gave me an idea how far apart the LEDs needed to be. 

I placed a piece of double sided tape over the dots on the paper. With tweezers, I placed each LED on the tape, centering them on the dots. This was easy as there is a notch at the centre of each LED. Once I had them arranged as I wanted, I tinned the LEDs. I soldered a piece of solid 30AWG wire cut long enough to bridge the positive side of both LEDs. This wire will eventually go to the blue common positive of the DCC decoder.

I soldered 2 more wires to the negative side of each LED. Then, I soldered a 1k resistor to each of the negative wires. At the other end of the resistor, I twisted the leads together and soldered them. This is where the white and yellow wires will be soldered for the front and rear respectively. 

I tested the fit of the LEDs and adjusted things with a pair of tweezers until everything lined up. After painting, I will secure the LED-resistor assembly to the inside hood of the loco with some Aleene’s Clear Gel Tacky Glue. This will fill the gap between the two LEDs ensuring the negative ends do not short out. 

That's it! Now to paint the locomotive and do the final installation of the lights. I will use some of the Aleene's Tacky Glue to create lenses for the lights when all painting is complete.

Now on to a harder application like lighting in my Walthers American Crane or some ditch lights with those tiny 0402s.

Don't be intimidated by these tiny things. A little practice and you can solder them up without issue.

Nice photos!

Greg  - nicely done and the photos are very good!

You may want to consider using SMT resistors, too, as you can get a really small package.

Keep up the good work!

dave

Plus 2 for SMT Resistors

Greg

Nice job and nice to see another convert to the world of surface mount LEDs.  SMT resistors can be a fiddle and I will often use a small piece of PCB to keep them in place. 

I have  found that hot melt glue works well for fitting both the LEDs and other components. On other occasions I will use Micro Scale Kristal Clear.

A guy in the UK uses black plumbers putty which stays pliable and cuts out any light leakage but I have yet to find a source for that in my part of the world.

How Small is Small

There are actually TWO 0402 SMC packages: one based on Metric units [0.4 mm × 0.2 mm (0.0157 in × 0.0079 in)] and one based on Imperial units (0.039 in × 0.020 in [1.0 mm × 0.5 mm]). It gets a little more confusing as the 0402 Metric package type is identified as Imperial 01005 and the Imperial 402 package is identified as Metric 1005.

I bring this up as I think from your pictures that you are working with 0.039 in × 0.020 in Imperial 402 parts (although your lead picture does show a metric 402 part). If you were working with Metric 402 parts the width of the parts would only be twice the width of the 0.1 mm wire you are using. So there are two standard SMD packages smaller than those you are working with. Grab you micrometers and check it out.

Well Ken, that throws a

Well Ken, that throws a wrench into the works. I'll have to take some measurements tomorrow. Who knew? Well, you did obviously.

Nicely done.  I hit my limits

Nicely done.  I hit my limits at the 603 level. I have, however, found pre wired 402s on EBay for a reasonable price.

Size

I would expect anything coming from China would be the metric 0402.

Greg states he is using the 1206 (1.2mm by .6 mm, supposedly see later) for the headlights of the 44 tonner, not 0402.

Having two 0402 sizes (there are other similar labeled imperial sizes too) is another reason why we should switch to the metric system like the rest of the world.

A little digging makes me believe the 1206 in the first image is the imperial size with a metric equivalent of 3216, because if you look at the smaller dimension next to the ruler it is well above .6mm, and does look about 1.6 mm and looks almost as tall as the 3014 (3.0 x 1.4 mm) next to it, so I could believe it to be 3.2 mm.

0402's come in real handy for

0402's come in real handy for running lights and step lights too:

I also used them for the platform lights, which work really well representing fluro tubes (when mounted in a hollowed out piece of brass tube).

Take it one step further

Greg; I did something similar, but went a step or two further; a company in London sells a product called "Bare Conductive", which is an electrical conductive paint.  LighthouseLEDS carries the micro resistors.

I installed 2 of the SMD LEDS in the back wall of an SD40-2 cab, painted the circuit on the walls, installed a micro resistor in each leg of the LEDs, then used CAA to attach the necessary wires from the decoder to each leg.  The LEDs put a nice glow behind each of the number boards...

JimMc

The glue

Not having used the glues mentioned above, I thought I would share what Jim Hinds of Richmond Controls (where I've purchased my SMD LEDs) recommends for glue.

Canopy Glue Formula 560

He says it dries perfectly clear and many use it for the lens itself as Nelson indicated above. It can also be tinted using craft paint used for stained glass windows if you want brake light lenses to be red for example. The setup time on it is also relatively long to give you enough time to fiddle with these very small components.

Seriously series

Seriously series shall need one less resistor; fun with alliterations.  

I've already wired 5 SMD LED's in series each drops about 2.5 to 3.2 volts (depending on the desired current) so the resistor value needs to be changed to accommodate the desired current. Also the supply voltage needs to be sufficient to overcome the total voltage drop. If the LED's drop around 2.5 volts each then the supply will need to be greater then 12.5 Volts plus whatever is needed for the ballast resistor.  If the LED's drop around 3.2 volts each then the supply will need to be greater then 16 Volts plus whatever is needed for the ballast resistor. The O gage layout I had worked on for a friend was supplied with 24 Volts which was converted to AC with the Lionel equivalent of our DCC system and I had to bridge rectify that to reconvert to DC; which also dropped another 1.4 volts but there was still enough potential remaining to produce great lighting. 

Be well & Have fun!! 
Rick

Greg, I don't know what part of the world you live in but Amazon has a black epoxy putty.

https://amzn.to/2IHurb2

Grainger sells a black gasket sealant.

https://www.grainger.com/product/PERMATEX-Gasket-Sealant-2GXY1?s_pp=false&picUrl=//static.grainger.com/rp/s/is/image/Grainger/2GXY1_AS01?$smthumb$

Plumber's putty

@DSteckler, neither of those items are like plumbers putty, since they both harden.  The advantage of plumbers putty is that it stays soft and pliable, meaning you can remove it if desired/needed.

I have not seen black either, just gray, as usually you don't want to see the putty when you seat the drain and tailpiece into the sink, so if it squashes out black would be much more noticeable than the gray.

Lowes or Home Depot

Lowes or Home Depot sell a flexible putty for sheet metal duct work.  You can buy a block of it for a few dollars and it lasts a long time.   http://www.homedepot.com/p/Gardner-Bender-Duct-Seal-Compound-1-lb-Plug-1-Each-DS-110/100212441

-bill

Color of the putty

The duct putty might be an alternative, will have to look at in the store to tell the color for certain, definitely looks darker than the plumbers putty.

The darker it is and hence the search for black is to help absorb the light out the back of the LED to prevent light going from where you don't want it.

I have lighted the Bachmann Parking Garage, but the LEDs shine through the back of the LED and through the ceiling to the floor above.  Only really noticeable on the top floor.   I just put the LEDs in temporarily so haven't done anything to prevent the light leakage yet and for that application putty would probably be too thick anyway.

Thanks Greg

I have a Bachmann 70T that I am less than pleased with the light output on the headlights.  A switch to these LED should fix that problem.  Thanks for the primer.

Marc Simpson

SMD LEDs Time and Effort

It's nice that you have the skills to solder magwire onto an 0402 SMD LED, but what a waste of time and eye sight health.  Why not just order them with wires already attached?  Besides being cheap, the saved time can be spent on the layout.

Another source of inexpensive pre-wired LEDs

Another source of relatively inexpensive pre-wired LEDs is from an eBay seller out of Germany, know as LEDBaron.

I have purchased many of their warm-white 0402 LEDs and also a few red ones for class lights. In every case I've been completely satisfied with their products. No affiliation other than being a happy customer. Note that the USPS wants a signature for overseas mail pouches.

Larger LEDs, 0603 and 1206 I buy from US electronics suppliers and I have no difficulty soldering my own wires.

By the way, instead of wiring LEDs in parallel, try hooking pairs in series. The single current-limiting resistor will thank you. Even in O-scale I often wire headlights in series and use a 1000 (1K) ohm resistor. The headlights are more than sufficeintly-bright.

In the days we only had incandescent lamps, we wired them in parallel. That is no longer necessary nor optimal with LEDs. That said, only connect two LEDs in series because they each drop about 3 Volts. If you hook 5 in series, odds are that none of them will light up in your locomotive or building when powered by 12 Volts.

Bob

Liquid electric tape as a replacement

for the plumbers putty, 

https://www.homedepot.com/p/Gardner-Bender-4-fl-oz-Liquid-Electrical-Tape-Black-LTB-400/100119178

The Whole Thread

Returned to the hobby after retirement (N scale).  I have recently been enlightened to the SMT for a couple of Steamers that did not implement the tender light.  "Fun with SMD LEDs" has enlightened me to smaller components, and the comments to SMT process and components.  But, the real eye opener was the use of glues for Lenses (and/or light piping in confined space?)

Thank you all for continuing my education.

Why the Red LED's?

This has  something to do with LED's. I like the idea of the smaller one for sure. My question is why are some of you using red in the class lights? In the real world, we only turned on the red class lights when we were running light engines or pusher service and used them for the rear marker. Marker lights were either white for an extra scheduled train and the green used for a regular scheduled train, so that operators would know what train you were, so he could clear you, when he observed the red markers, from the block you were occupying. These were used under train order or Dark territory.

JT

Red lamps displayed by helper locomotives

In certain eras, red class lights were displayed to the rear by a helper locomotive shoving a train. They served the same purpose as red marker lights on a caboose. 

On a lead locomotive, white class lights indicated that the train was an extra, i.e. one not scheduled in the timetable.

Green was used in TT&TO operation to indicate that there would be one or more extra sections following closely behind. If a train received a train order to meet #75 at a certain place, that train would need to stay in the clear until all the sections of #75 had passed. The last section of #75 would not display green class lights indicating that it was the last section. Extra sections were sometimes operated when tonnage exceeded that which could be handled by locomotives normally assigned.

Possible problem with Plumber's Putty

I am not sure of the reason, but Plumber's Putty is not recommended for use with plastic pipe.  Plastic pipe is a different plastic than the polystyrene used in our models but both are plastics..  I have used  DAP Kwik Seal kitchen and bath adhesive caulk to hold and seal lights and wires with good results.  It remains flexible, with water cleanup and is paintable.  It can also be used to seal speaker enclosures and the wires from the speaker enclosure.  It is white, but can be painted if needed.  (For sealing plastic pipe, Teflon paste is used, but it is not useful for this application.)

Bill. 

re: Plastic pipe and plumber's putty

Plastic pipe is PVC (white) or ABS (black)  and they don't respond the same to cements or putty. 

I'd be wary of anything incompatible with ABS, as the S= styrene  and the A= acrylic ...  [acryrlonite butadiene styrene] and most of the materials in modeling are styrene or acrylic based.

I'd consider latex caulk colored black or dark brown if I wanted a pliable masking agent.  A hand-applied enamel paint might also do.