Converting an Athearn Locomotive to LED Lighting

  • 01 of 05

    Removing the Incandescent Bulbs

    LED Lights
    LED headlights add a realistic look and long life to Athearn locomotives. ©2015 Ryan C Kunkle, licensed to, Inc.

    Athearn produces a great variety of HO locomotives with outstanding detail and reliable performance. But one common complaint among modelers is that they continue to use 1.5-volt incandescent bulbs for their lights.

    While the lights provide a nice color, they can burn out quickly. Fortunately, these locomotives can be converted to LED lights. LEDs will last a lot longer and reduce the voltage draw - which can be significant on a layout with a lot of locomotives.

    These techniques will work on other...MORE brands of locomotives as well. While each installation can be a little different, the basic steps will be the same. The model shown in this conversion is an older Ready-to-Run SD40. For this installation, both LEDs and ​fiber optics will be used.

    The first step is to remove the light bulbs. The small bulbs are held in place with glue on the inside of the shell. This glue is water-soluble. Just place a small drop of water on the glue and let it sit for about a minute. You should be able to gently pry the bulbs loose without and problem.

    Disconnect the wires from the PCB board. You can use the same tabs on the board for the new LEDs. If you are installing a DCC decoder, you can use the tabs on the board, or just hard wire to the white, blue and yellow leads on the decoder. 

    Continue to 2 of 5 below.
  • 02 of 05

    Pre-wiring the LEDs

    LED bulbs
    It is easiest to wire the LEDs and resistors before installing in the model. ©2015 Ryan C Kunkle, licensed to, Inc.

    Unlike incandescent bulbs, LED's are polarized. Each LED has a positive and negative lead.

    The positive (+) lead is called the anode and if the LED has leads attached will be the longer. Other LEDS, like surface mount style, will have a flat spot or mark on the + side. 

    The negative (-) side is called the cathode and will be the smaller of the two leads. It is important to wire the LED's correctly. 

    You'll also need a resistor to reduce the voltage sent to the LED. You can wire...MORE the resistor to either side.

    For most model train applications, the combination of LED and resistor shown here will work very well. LEDs are T1 3mm "sunny white." (To better mimic incandescent bulbs, look for a sunny or warm white LED. Others will have a more bluish hue.) Pair these with 1k ohm 1/4 Watt resistors. 

    It is easiest to wire the LED's for the headlight and backup light before installing in the locomotive. You can greatly shorten the leads of most LEDs. Just clip them to the desired length with wire cutters. Space is at a premium inside most locomotives, use as little lead as possible.

    Place the LEDs back to back and solder the anodes together. Then attach a short length of wire to connect to the PCB or decoder. If hard wiring to the decoder directly, this should attach to the blue lead.

    Next, wire a resistor on to each of the cathodes.

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  • 03 of 05

    Wiring the LEDs to the PCB

    LED wiring
    Connect the LEDs to the PCB or decoder. Secure all connections with heat shrink. ©2015 Ryan C Kunkle, licensed to, Inc.

    Next, the LEDs need to be connected to the locomotive. Again, you can use the PCB board in the locomotive or go directly to a DCC decoder. It is best to plan ahead and think about how you will connect the fiber optics to the LED and the LED to the board so that you can still get the shell on/off the locomotive.

    For the PCB, connect the anodes to the common post and the two cathodes to the headlight and reverse light posts respectively.

    For a decoder, use the white wire for the headlight, yellow...MORE for reverse light cathode and blue for the anodes.

    Slide a piece of heat shrink tubing over the wires before soldering the connections. Then position the tubing over the bare wire and use the edge of your soldering iron to shrink it around the joint. Use liquid electrical tape over the anode connection. Space is tight inside these models- don't take any chances with bare connections. 

    If you are adding additional lights (ditch lights, warning lights, marker lights, etc.) simply repeat these steps and use the appropriate leads.

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  • 04 of 05

    Attaching Fiber Optics

    Fiber Optics
    Use more heat shrink to attach fiber optic strands to the LEDs. ©2015 Ryan C Kunkle, licensed to, Inc.

    Use fiber optics to carry the light from the LEDs to the lenses. For most Athearn engines, .040 strands will work well. 

    This is where the installation gets a little more difficult. You'll have to plan ahead to determine the best way to go about the installation in your locomotive. For this application, it was easiest to test fit the strands, install them in the locomotive, make the connections with the shell in place (keeping the dynamic brake hatch off) and then trimming the fiber optics to...MORE length. 

    You may find it easier in some models to connect all of the fiber optics first, attaching the LED assembly to the body and then making the connections to the PCB / decoder last.

    First, cut each fiber optic strand to an approximate length to run from the lens to the LED. Leave a little extra.

    Bond the ends of the fiber optics together with more heat-shrink tubing. For paired lights, use a small band of tubing to first join the two leads together with their ends even. Then use a larger diameter tubing to connect the pair and the LED. The tubing should fit snugly around the LED. Avoid using much heat on the tubing to shrink as it could damage the fiber optics. 

    You'll be able to take the strands off the LEDs and reattach if needed as you assemble the model.

    Paint the fiber optic strands black to prevent light from leaking through fans, cab windows or other openings in the body.

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  • 05 of 05


    Once the body is assembled, trim the LEDs to length and install plastic lenses if desired. ©2015 Ryan C Kunkle, licensed to, Inc.

     With the body assembled and everything connected inside, the last step is to finish the lights themselves.

    Trim the fiber optics to length. Hold the tip of your soldering iron near the end of the strand and the end should flare out. If this gives you enough of a lens appearance, you're good to go. You can also use clear plastic lenses from Details West in the openings themselves. Trim the fiber optics so they end just inside the housing and glue the plastic lenses in front. 

    Use a piece of...MORE tape to hold and position the tiny lenses in place.

    After you've done a few of these conversions, you'll find the process goes fairly quickly. Buying in bulk, the cost of materials is well under $2 per locomotive - about what you'll spend on replacement bulbs each time.