Support - Lighting

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Overview - Understanding Light Functions

TCS decoders follow the NMRA standards and specifications for lighting functions (Document S-9.1.1), including the color code. The full list of NMRA-standardized wire colors for lighting can be found below, as well as at the previous link.

While it may not make sense on some products without wires, it can be more complicated to define functions as "functions" due to the confusion between sound functions, light functions, and physical buttons on your handset.

To clarify, we like to delineate numerical functions like this:

  • A "Button" with a number (0 -> 28) corresponds to the numbered "buttons" on the throttle or other controlling devices. On a physical throttle these would be the numbered buttons on the handheld. Similarly, in JMRI Decoder Pro this is the throttle you can pull up and use from your computer. If you use a cellphone or tablet, these are the buttons you can press on your screen.
  • A "Function" is typically defined as an electrical output from a decoder. Sometimes, "functions" can be referred to as "outputs" for better clarity and to limit the confusion with sound functions. Numerals are assigned to each output to distinguish it from the rest. On an 8 function decoder, you have two "0" functions for forward and reverse per the NMRA standard. (0F and 0R count as TWO functions. 2 + 6 = 8)
  • A "Function" and a "Button" are NOT required to be linked together. Functions may be assigned to other buttons using the remapping CV's. As an example, for Function 1 and Function 2 these CV's are 35 and 36 respectively. A value of 4 in both of these CV's will remap both of the function outputs to respond on Button 1 on your controller. HOWEVER! A "Function" will ALWAYS retain the same lighting effect CV as its output number. For example, CV51 corresponds to Function 1 and CV52 corresponds to Function 2. Regardless of what button these function outputs are mapped to, their effect CV's will continue to reflect their "Function" number.

TL;DR: "Function" = electrical output from decoder | "Button" = physical numbered button on controller

In the case of a sound decoder, which has both LIGHT functions, as well as SOUND functions, there is an added level of complexity. In this case, we like to use the term "OUTPUT" to refer to a lighting function, and the term "FUNCTION" used to refer to sound operations.

All light functions can be remapped or reprogrammed for your desired operation. For more in-depth details on function remapping and output assignment, continue reading below about Function Remapping.

Decoder Wiring Color Code

The NMRA Standard S-9.1.1 defines DCC decoder wiring colors to be as follows:

NMRA DCC Decoder Wire Color Code
Wire Color [DCC] Function/Application
Red Right hand (engineer's side) rail power connection.

Could also be the center rail in 3-rail applications, or overhead catenary wire

Black Left hand (fireman's side) rail power connection.

Could also be the outside rails in 3-rail applications, or overhead catenary wire

Orange Positive (+) polarity Motor connection (for "forward" operation)
Grey Negative (-) polarity Motor connection (for "forward" operation)
Blue Common positive (+) voltage source for lighting and other options
Black & White


Common ground (-) for decoder and/or [lighting] functions
White Function 0 Forward - Forward Headlight
Yellow Function 0 Reverse - Reverse Headlight
Green Function 1 (Output 3)
Violet Function 2 (Output 4)
Brown† Function 3 (Output 5)
Pink† Function 4 (Output 6)
Pink & Purple


Function 5 (Output 7)
Green & Brown


Function 6 (Output 8)

NOTE: This is not a complete chart of all wire colors used by TCS on our decoders. The full chart can be found on the page TCS Wire Color Code.

"Manufacturers may use any colors or other means to identify each wire such as a tag but each wire must be identifiable and this must be documented in the installation instructions. Black, red, orange, gray or blue of the same shade as the power common may only be used as defined in this table" The colors used by TCS to identify these outputs on all decoders are identified here.

"The wire color for "Ground" may be substituted, but must be documented. All efforts must be taken by the decoder manufacturer so as not to confuse the decoder ground with any other input or output."

Wiring Lights to a TCS Decoder

The precise wiring of your locomotive's light functions is ultimately at the discretion of the end user. However, a few rules do apply, and these rules may change depending on the type of light you intend to use. Learn more below!

Lights - The Rules of Wiring Incandescent Bulbs

When using incandescent bulbs, observe the voltage rating - 12V bulbs must be connected to the 12V supply. Incandescent bulbs rated for 1.5V may be connected to 12V, but only through a resistor with appropriate ratings for the rated current of the bulb; alternatively, a TCS VR1.5, or an on-board 1.5V source may be used to provide a regulated 1.5V supply for all of your lights. Some TCS motherboards have dedicated 1.5V power supplies on-board for these bulbs, but not all motherboards. Additionally, some motherboards have dedicated contacts for "Bulbs." These dedicated bulb outputs bypass the on-board resistors for use with LED's which would otherwise prevent the bulb(s) from lighting.

If you are installing an Athearn locomotive of an older vintage which has not had the factory bulbs replaced, you should use the 1.5V power supply as the positive voltage source for your lights. Athearn throughout most of their history has used 1.5V incandescent bulbs, with only a very recent transition to LED's. As such, the 1.5V power supply indicated on the motherboard, plus any correspondingly labeled "Bulb" pads are to be used for these models. The GEN-MB1 and RTR-MB1 motherboards designed for use in the Athearn Genesis and Ready-to-Roll/Blue-Box lines include onboard 1.5V power supplies for this reason.

Incandescent bulbs, unlike LED's, are not polarized, meaning they can be connected with either wire to either pad. It is common for a locomotive manufacturer to bundle together one wire from each light and tie it to the source, then run a single wire from each light to the functions. The same applies to a replacement motherboard. When wiring a TCS motherboard, follow the same practice, connecting one wire from each incandescent light to the appropriate Voltage source, and the second wire from each light must then be run to its own respective function output as described in our Understanding Light Functions section.

Question: "When measuring the voltage for a lighting function, what level should I see?"

When measuring a function output from a decoder or motherboard between a SOURCE (E.G. "Blue" / "12V" / "V+" / etc.) and the output pad, note the following:

  • DC Voltage must be selected on your multi-meter
  • DC Voltage can only be observed while the decoder is POWERED, and the FUNCTION IS TURNED ON using your throttle.
  • The DC Voltage observed will be the voltage developed across the LOAD on the output you are measuring. What is the load, you ask?
    • If no physical lamp is connected to the output you are measuring, your meter IS the load - You will observe the full voltage from the source in this condition.
    • If a physical lamp is connected to the output you are measuring, your meter will read the voltage dropped across that lamp. In the case of an incandescent bulb, this should be the rated voltage.

Question: "My readings are not matching what I expect them to be. What should I do now?"

Visit the Multimeter Troubleshooting section to help diagnose the issue.

Lights - The Rules of Wiring LEDs

When using Light Emitting Diodes (LED's), you must always include a resistor in series with the Cathode to limit current UNLESS your TCS product has on-board LED support. Refer to your decoder literature, wiring diagram, or the silk screen on the board itself for LED connection points (if applicable).

If using Light Emitting Diodes, polarity must be observed, as a reversed connection will not work. Diodes have two connections known as the Anode, which is a (+) connection, and Cathode, a (-) connection. When working with decoders, the Anode(+) connection is to be connected to a common voltage source, and the Cathode(-) connected to an individual function output. These connections will be noted in your decoder literature or on the silk screen of the product itself. The NMRA determined that DCC decoders are to be designed as "Common Anode" devices, meaning there is to be ONE, COMMON, POSITIVE voltage source, and individual returns to ground(-).

BLUE is the color designated by the NMRA to be used for the common Positive Voltage Source. On decoders, this can be designated as a Blue wire, "BL" or "+", or similar. As many lighting functions as needed are to be wired to this one point. Some decoders have multiple connection points for ease of installation. TCS decoders, unless otherwise specified, use an un-regulated +12V DC power supply to power the lighting effects. This power supply is fed directly from the rectified track voltage; therefore, the voltage of this supply will vary based on your track voltage and can be assumed as ~1.5V less than your AC track voltage.

Each function on a decoder is given an associated color and function number to serve as a return to ground. When using LED's, these connections must be made to the cathode (-). If your decoder requires external resistors for use with LED's (not LED-ready), you should always connect the resistor on the cathode (-) side of the LED to prevent current surges into other connected functions as a result of a lighting effect cycle or a function turning on or off.

LED's are current-driven devices, not voltage-driven devices. This means that the voltage across your LED will always remain constant as determined by the LED's voltage rating itself. The brightness of an LED will be determined by the current flowing through the circuit. The current passing through a lighting function is determined by the resistor value used. Following Ohm's Law, we know that the current is directly proportional to the voltage, and inversely proportional to the resistance. If you know the voltage rating of your LED, subtract that from the total voltage in the circuit (we can assume 12V) and divide that value by the resistance to yield your current. All of TCS' LED-ready products (that includes decoders and motherboards) are fitted with 1000 Ohm resistors. This value of resistance yields fine results with just about any LED. If you are using aftermarket LED's, it is recommended that said LED be rated between 1.5V and 6V, with the typical rating being 3V.

Question: "When measuring the voltage for a lighting function, what level should I see?"

When measuring a function output from a decoder or motherboard between a SOURCE (E.G. Blue/12V) and the output pad, note the following:

  • DC Voltage must be selected on your multi-meter
  • DC Voltage can only be observed while the decoder is POWERED, and the FUNCTION IS TURNED ON using your throttle.
  • The DC Voltage observed will be the voltage developed across the LOAD on the output you are measuring. What is the load, you ask?
    • If no physical lamp is connected to the output you are measuring, your meter IS the load - You will observe the full voltage from the source in this condition.
    • If a physical lamp is connected to the output you are measuring, your meter will read the voltage dropped across that lamp. In the case of an LED, this would be 3 Volts in most cases.

Question: "My readings are not matching what I expect them to be. What should I do now?"

Visit the Multimeter Troubleshooting section to help diagnose the issue.

Calculating Resistor Values

Need to calculate a resistor value for your circuit? Make sure you have the voltage and current specs for your lamp, and then click the following link for a handy-dandy tool! [TODO Series Resistance Calculator]

WOWSound - Light Mode and Sound Mode

Question: I hooked up my lights on my WOWSound decoder but I cannot turn them on. What gives?

NOTE: If you are looking for assistance or advice on wiring your locomotive, see the sections below for wiring LED's or incandescent lamps.

WOWSound decoders have two operational modes: Light Mode and Sound Mode. When first powering up a WOWSound decoder, it will default to Sound Mode. In order to access your light functions beyond F0, you must enter Light Mode. (Unless otherwise user-configured)

To toggle operational modes, you must press Button 8 on your controller twice in rapid succession. You will hear an announcement from Audio Assist® announcing the active mode. In order to change back, just press button 8 twice again. If you switch too fast, however, the decoder may register 4 presses and enter the Audio Assist® program.

In sound mode, you can use buttons 0-28 to control sound functions. In Light Mode, you can use buttons 0-12 to control lighting functions. Both modes can be remapped using Audio Assist or CV programming, but you should refer to your decoder literature for the default mappings. By default, Light Mode buttons will correspond directly to their numbered function output unless otherwise programmed. By default, ONLY function 0 will respond to commands in both Sound Mode and Light Mode. In order to use any other function button in both modes, that button must be "dual-enabled" using CV programming. For assistance on CV programming function buttons into dual-mode, visit the Guided Programmer for your decoder type:

Programming Tools

Question: Function 2 doesn't work?

Most likely, lighting Function 2 of your decoder is working. Some command stations and throttles such as Digitrax set Button 2 as a momentary function (not latching). You can confirm this by holding the button down to see if your light remains on.

Okay so how do I fix that?

The simple solution is to remap your light to another button. Otherwise, the instruction manual for your throttle or command station should tell you how to change the momentary function to a latching one.

To learn more and see a demonstration of Light Mode and Sound Mode, check out our video on WOWSound Operational Modes:

Setting Up Lighting Effects

The Lighting Effect CV's are used on decoders to set the lighting effect for each of the lighting outputs. The value in these CV's sets the active lighting effect and the active direction. Consideration must be taken to choose the correct value which includes BOTH factors when performing programming of a lighting effect.

Below, you can find solutions to our most-commonly-asked lighting configuration questions.

Setting up Ditch Lights

Ditch lights are very common on modern Diesel locomotives. Many models available in the market today come factory equipped with at least one pair of operational ditch lights. By default, TCS decoders are configured to output a constantly bright light on all lighting functions. If the road you are modeling has constantly bright ditch lights that simply turn on and off, you can ignore this section. If you are modeling a road which has alternating/blinking/flashing ditch lights, this section below will give you the CV values to program those lights.

Question: How do I turn on my ditch lights on my TCS WOWSound decoder?

Hold your horses! Before we get to turning on the lights, lets make sure they are connected and programmed! To make sure everything is in good working order, let's go through a couple of setup steps. First, TCS recommends connecting your ditch lights to the following lighting outputs - Function 1 & Function 2 for forward, and Function 3 & Function 4 for reverse (if applicable). For instructions on literally hooking up and wiring your lighting functions to a TCS decoder or motherboard, read the sections above for Wiring Lights to a TCS Decoder with either LED's or Incandescent Lamps.

Once you have your ditch lights physically connected, we can get down to programming! The easiest way to set up your ditch lights is by using TCS' quick preset for ditch lights. Most users want their ditch lights to flash if the Horn button is pressed. By using this preset, a WOWSound decoder will operate in this way. The quick preset will automatically perform the following sequence. You do NOT need to manually enter this sequence unless something goes wrong.

STANDARD CONFIGURATION: Two Omni-Directional Ditch Lights Controlled by Button 1

To set up GREEN and VIOLET: (Turn on/off with Button 1 [in light mode for sound decoders])

  • CV35 = 4 - Function 1 on/off with Button 1
  • CV36 = 4 - Function 2 on/off with Button 1
  • CV51 = 42 - Ditch Light Side 1 (Bi-Directional)
  • CV52 = 43 - Ditch Light Side 2 (Bi-Directional)
  • CV124 = 8 - BLINK ON BUTTON 2 ONLY

FOR SOUND DECODERS, To set up Button (2) to work in both light & sound mode, program the following sequence in order:

  • CV201 = 4
  • CV202 = 14
  • CV203 = 2
  • CV204 = 11 - DUAL ENABLE BUTTON 2

NOTE: All of the above configurations will be set automatically if you use the CV 8 Macro for Ditch Lights. The ditch lights will turn on and off using Button 1 (in Light Mode for sound decoders) and will not turn off in the reverse direction.

ADVANCED CONFIGURATION: Four Directional Ditch Lights Controlled by Button 1

For models which have four ditch lights - one pair in the front and one pair in the rear, the above sequence needs to be modified. For example, the lights may need to be set to be directional. To set this up, use the following programing steps:

To set up GREEN and VIOLET: (Turn on/off with Button 1 [in light mode for sound decoders])

  • CV35 = 4 - Function 1 on/off with Button 1
  • CV36 = 4 - Function 2 on/off with Button 1
  • CV52 = 11 - same as above
  • CV124 = 8 - BLINK ON BUTTON 2

To set up PINK and BROWN: (Turn on/off with Button 1)

  • CV39 = 4 - Function 3 on/off with Button 1
  • CV40 = 4 - Function 4 on/off with Button 1
  • CV54 = 27 - same as above

FOR SOUND DECODERS, To set up Button 2 to work in both light & sound mode, program the following sequence in order (If you programmed CV8 to 10 already, you do not need to program the following!):

  • CV201 = 4
  • CV202 = 14
  • CV203 = 2
  • CV204 = 11

Modification to Use Button 0 (Headlight)

If you would like to have your ditch lights operate on Function 0 (headlight) rather than Function 1 in light mode, set the following during or after the previous sequence:

  • CV35 = 1
  • CV36 = 1
  • CV39 = 1
  • CV40 = 1

Modification to Allow All Horn Sounds to Blink Ditch Lights (WOWSound Version 4 and Older)

TCS WOWSound decoders offer 3 horn/whistle buttons by default on Buttons 2, 3, and 4. If you would like to set up the ditch lights to operate when ANY of those buttons are pressed, you need to modify the sequence(s) above with the values below during or after the previous sequences:

  • CV124 = 56 - Blink Ditch lights on Button 2 OR 3 OR 4.
  • CV201 = 4
  • CV202 = 14
  • CV203 = 2
  • CV204 = 59 - Dual-enable Buttons 2, 3, and 4

Now that we have completed our programming, we can turn the lights on! If you have configured your ditch lights to operate with the headlight, just turn your headlight on and you are done! If you have a TCS WOWSound decoder and have programmed your ditch lights to a different function button, you need to go into Light Mode.

Setting up Directional Marker Lights

Question: How do I set up directional marker lights on my passenger service locomotives?

By default, (with exceptions in the OEM market of course) the default lighting effect for Function 1 and up is "Constant Bright" in both directions. This means that if you turn on a lighting function number 1 or greater, it will come on at full brightness, and will remain that way in either direction until you turn it back off. A common request we receive is to set up marker lights that are active in the opposite direction of travel. The directionality of lighting effects is based on the value entered in for that lighting effect generator. The Lighting Effect CV's can be programmed with values to determine the lighting effect as well as the direction of that lighting effect. For example, a constant bright light in the forward direction equates to a value of 0; in the reverse direction, this value is 16, and for both directions (the default value) is 32.

For the above case, light functions tied to the lights physically pointing opposite the direction of travel need to be programmed with the value which corresponds to the direction of travel. For example, the lights on the rear of the engine would be programmed to be ON in forward, and the lights on the front of the engine would be programmed to be ON in reverse.

Please consult the Full List of Lighting Effects for your decoder type and version for the full chart of available lighting effects and the corresponding directional values.

Setting up "Constant Dim" Lighting Effects

The "Constant Dim" lighting effect is useful in applications where you may not want to have a lighting function be active at full brightness at any time. Examples may include passenger car lighting, directional markers, a cab light, or plenty of other circumstances. In order to use and customize the "Constant Dim" lighting generators, you need to do two things:

  1. Assign a Constant Dim lighting generator to a Function Output.
  2. Configure the Constant Dim generator to your desired brightness level (optional)

The exact performance of a constant dim lighting effect will vary based on factors such as:

  • The rated voltage of the lamp (LED or incandescent)
  • The series resistance (if applicable)
  • The output capacitance (if applicable)

It is recommended to use a capacitor in parallel with your LED lights when using the constant dim lighting effect if you intend to take videos of your models. Photosensors on cameras will often pick up on the PWM when using LED's and the constant dim lighting effect, resulting in a flicker on the video. This same flicker is not visible to the naked eye, and is as such not normally an issue. This issue is also not typically a problem if you use incandescent bulbs.

WOWSound Version 4 (and older) and TCS Non-sound

Note that in TCS WOWSound Version 4 (and older) decoders, as well as the non-sound product line, we offer FOUR independent dimness generators. Any lighting output can be assigned to have its own "dimness" generator assigned, or the same generator may be assigned to multiple functions simultaneously depending on your needs. By applying the same dimness generator to multiple lighting effects, those lighting effects will operate at the same level of dimness relative to the configurable setpoint.

Step 1: To assign a constant dim lighting effect to an output, program the Lighting Effect CV for that output using the corresponding value found in the Full List of Lighting Effects based on the generator number and active direction you desire.

Step 2 (optional): Each of the constant dim generators can be individually reconfigured using individual CV's. Program the corresponding "dimness level" CV for the generator you selected to change the level of dimness.

Note: There are also two other "dimness" generators for use in Rule 17 applications, allowing you to independently configure the dimness level of both headlights in addition to the four constant dim generators. The chart below shows all of the CV numbers and corresponding generator numbers which you can configure.

Constant Dim Lighting Effect Configuration
CV Number Dim Generator CV Range Default
CV 156 FWD Headlight 1-30 1
CV 157 REV Headlight 1-30 1
CV 64 Constant Dim 1 1-30 6
CV 153 Constant Dim 2 1-30 5
CV 154 Constant Dim 3 1-30 5
CV 155 Constant Dim 4 1-30 5

WOWSound Version 5

Coming Soon!

Function Remapping

Overview - Function Remapping

NOTE: This section only covers the remapping of LIGHT functions, not SOUND functions.

Function mapping of lighting outputs can be done via the programming of Configuration Variables or via Audio Assist on WOWSound decoders. Your decoder literature pamphlet, as well as the programming resources available on this site will show the CV's and values that correspond to the function outputs and function buttons.

In the NMRA Standards document S-9.2.1 (currently under revision), the DCC standard for packet transmission (that is, the communication over the rails), function buttons for lighting are separated out into three function groups. Functions 0-4 make up the first group within the packet, and Functions 7-12 are part of Group 2. Group 2 is further divided into Lower and Upper groups, with Function 5 though Function 8 making up Lower Group 2, and Function 9 through Function 12 making up Upper Group 2. Note that in this context, the word "Function" is being used to refer to button numbers used to control the decoder, not actual output from the decoder.

Function Remapping - TCS Non-sound Decoders; WOWSound Version 4 and Older

In TCS non-sound decoders, as well as WOWSound Version 4 hardware and older, if a function is going to be assigned to respond to a command in one of these groups, it needs to be configured in that corresponding CV. Below is a chart identifying the CV numbers and corresponding values used to map a lighting function to a button number.

Function Remapping
Group A (Button 0 through Button 6) Group B (Button 7 through Button 12)
Button 0F 0R 1 2 3 4 5 6 Button 7 8 9 10 11 12
Value 1 2 4 8 16 32 64 128 Value 4 8 16 32 64 128
Use values for buttons from above to program CV numbers for function outputs below

A value of 0 removes control of that output from any button within the group.

Function 0 cannot be remapped above Button 6 in decoders of the defined type(s) which

use(s) this chart

CV Output No. Default CV Output No. Default
33 F0 FWD 1
34 F0 REV 2
35 F1 4 37 F1 0
36 F2 8 38 F2 0
39 F3 16 41 F3 0
40 F4 32 42 F4 0
43 F5 64 45 F5 0
44 F6 128 46 F6 0

As you see on the chart, Functions 1 - 6 have TWO CV's EACH. The CV on the LEFT of the chart can be used to assign a button from 0 - 6 to that function. A value of ZERO in any of these CV's will disable the function from responding to any button from 0 - 6. Along the RIGHT of the chart are the secondary CV's which correspond to buttons 7-12. By default, these CV's are 0. By programming a value to these CV's, a button or buttons can be assigned to activate the function from 7-12. Note that it is possible to have multiple buttons control the same function using this method if desired. It is suggested that only one CV for each function be programmed with a non-0 value to prevent de-synchronization or confusion.

Along the TOP of the chart are two sections with values from 1 to 128. The numbers from 0 to 12 listed above the values state what value would correspond to that button number. By programming the value listed below a button number, that button will be assigned the function whose CV was just programmed.

It is important to know the difference between a FUNCTION and a BUTTON.

  • A FUNCTION corresponds to a numbered function output and/or colored wire from the decoder. For details on which color of wire corresponds to a numbered function output, refer to the chart above, or the NMRA Wires and Connector Standards.
  • A BUTTON is located on your throttle or control device and does not necessarily directly correspond to any output from the decoder, as this can be configured.

Example: You are attempting to move a function to the higher function group. F2 -> Button 8. To do this, once again look at the chart. Function 2 has two CV's - CV36 and CV38. Button 8 is part of the higher functions, which would make use of CV38. Therefore, by selecting the value that corresponds to Button 8 (a value of 8), and programming that value into CV 38, Function 2 will now respond to Button 8. To finish the transfer, we need to clear the button from responding to Button 2. To do this, program CV 36 with 0. Now you are finished!

Function Remapping - WOWSound Version 5