I use 0201 or 0402 LEDs- about 2-3 cents each or so from many suppliers on ebay. You can pick your color, too. Then, I get SMD resistors, 2.2kOhm or 1.5kOhm or 3.3kOhm, again on ebay. Tin both contacts on the resistors and the LEDs. Stick them down on a piece of wood with double sided tape. Work fast with a small iron and fine diameter solder. Then take the leads from the decoder, and tin the ends. Next, put the resistor and LED touching each other. Clean the soldering pen tip, add a bit of solder, then touch it to the joint where the two parts are touching. This takes less than a second. The joint is very strong. Next, using a DVM with a diode tester, touch the outer contact of the SMD resistor with the BLACK test lead, and touch the open contact of the LED with the RED probe. If the LED lights, the RED end gets the BLUE wire (positive) from the decoder, or the positive contact pad if you are soldering directly to the decoder. If the LED does not light, just reverse the leads. It should light, unless it got overheated (they are pretty rugged parts). See the picture showing the connections. I double up the wires (blue and teal) on the same positive pad on my decoders for simpler wiring. Also, I have found that these LEDs just slip under the clear plastic lenses at both ends in Kato, Atlas, InterMountain and Arnold/Hornby diesels. So, by leaving the leads a bit longer, I can slip the light assemblies under the lenses, then close up the shell. Kind of "self-aligning".
