1. Application
Control Car, Coach or Special Model?
The application determines the connection, required space and necessary functions.
Control lighting, couplers and special functions digitally
Choosing Function Decoders: Lighting & Functions
Function decoders switch headlights, tail lights, interior lighting, cab lighting, couplers and effects without controlling a traction motor. This selection guide takes you from the vehicle and interface to the required output rating.
Digital functions without motor control
What Is a Function Decoder?
A function decoder receives digital commands from the track and switches electrical consumers inside a vehicle. Typical applications include headlights and tail lights in a control car, interior lighting, destination displays, cab lighting, digital couplers and special lighting effects.
Unlike a locomotive decoder, a dedicated function decoder does not contain a regulated motor output. It can therefore be smaller, less expensive or equipped with a particularly large number of switching outputs. Points and signals on the layout are normally controlled by a stationary switching decoder instead.
Before purchasing, check the interface, installation space, protocol, output type and current rating. LEDs require suitable series resistors. Incandescent lamps, couplers and relays can draw considerably more current and must not overload the decoder.
Seven decisions leading to the right version
Choose a Function Decoder Step by Step
2. Interface
Connector or Free Wiring?
Next18, PluX, 21MTC and NEM connectors must match the circuit board exactly.
3. Outputs
Count Every Function Separately
Independently switchable lighting groups normally require their own outputs.
4. Load
Calculate the Current Consumption
The individual and total current must not exceed the decoder ratings.
5. Output Type
Amplified or Logic Level?
Logic-level outputs cannot power electrical consumers without additional circuitry.
6. Digital Format
Match the Command Station and Decoder
At least one common protocol must be supported.
7. Additional Requirements
Check Energy Storage and Special Effects
Flashing lights, uncouplers, servos and energy storage require suitable connections.
Distinguish the purpose and installation location
Locomotive, Function and Switching Decoders Compared
| Decoder Type | Installation Location | Main Purpose | Motor Output | Typical Application |
|---|---|---|---|---|
| Locomotive Decoder | Locomotive or multiple unit | Motor and vehicle functions | Yes, regulated | Digitising a locomotive without sound |
| Sound Decoder | Locomotive or multiple unit | Motor, functions and sounds | Yes, regulated | Locomotive with driving and operating sounds |
| Function Decoder | Control car, coach or function model | Lighting and auxiliary functions | Normally no | Directional lighting, interior lighting and couplers |
| Switching Decoder | Under or beside the layout | Points, signals and accessories | No | Stationary solenoid accessories and relays |
| Servo Decoder | Vehicle or layout | Control servo movements | Servo pulse | Doors, couplers and moving models |
Rule of thumb:
A function decoder is a vehicle decoder without regulated motor
control. It is selected according to the electrical consumers, output
types and total load.
Three details for an initial selection
Which Function Decoder Fits My Vehicle?
Check the electrical ratings before connecting
Understanding Function Outputs Correctly
Amplified Outputs
They can switch suitable LEDs, lamps, relays and couplers directly.
Check
The current per output and permitted total current.
Logic-Level Outputs
They provide only a control signal and normally require an amplifier.
Check
The circuit-board documentation and external transistor circuit.
Common Return
Many decoders use a common positive connection for the function outputs.
Check
The wiring and polarity of the vehicle circuit board.
LED Outputs
LEDs require current limiting unless this is already provided on the circuit board.
Check
The series resistor, voltage and required brightness.
Uncoupling Mode
Time limiting or a kick function protects the coupler and decoder against overheating.
Check
The starting current and maximum activation time.
Function Mapping
Outputs can be assigned to function buttons, direction and operating conditions.
Check
The supported buttons and programming options.
Typical vehicle projects
What Can a Function Decoder Be Used For?
Control Car
Headlights and tail lights are switched according to the direction and selected function button.
Recommendation
Next18, PluX22, 21MTC or NEM 652 to match the circuit board.
Passenger Coach
Interior lighting, tail lights and destination displays can be controlled separately.
Recommendation
A compact wired or LED version.
End-of-Train Coach
Tail lamps remain digitally switchable independently of the locomotive.
Recommendation
A small decoder with only a few outputs.
Digital Coupler
Couplers require sufficient current and time-limited activation.
Recommendation
A high-current output with an uncoupling mode.
Special Vehicle
Cranes, doors, hazard lights and working lights can be operated individually.
Recommendation
Numerous outputs or a servo connection.
Garden Railway Coach
Large lamps and multiple electrical consumers require a higher current rating.
Recommendation
A robust large-scale function decoder.
Consider the component size and electrical consumers together
Choose Function Decoders by Gauge
Gauge N
Small Next18 or micro decoders fit inside control cars and illuminated vehicles.
Important
Component height and heat generation.
Gauges TT and H0e
NEM 651, Next18 and PluX12 are frequently used.
Important
The circuit-board pin assignment and installation orientation.
Gauges H0 and 0
NEM 652, PluX22, 21MTC and wired versions provide numerous outputs.
Important
Distinguish amplified outputs from logic-level outputs.
Gauges 1 and G
Higher currents and larger electrical consumers require robust decoders.
Important
The total current and track voltage.
Connect and test safely
Install a Function Decoder in Six Steps
Step 1
Open the Vehicle
Document the interface, wiring and electrical consumers.
Step 2
Measure the Current
Check lamps, LEDs and couplers individually.
Step 3
Check the Decoder
Verify the connector, outputs and digital protocol.
Step 4
Install with the Power Off
Insulate the wiring against short circuits.
Step 5
Use the Programming Track
Test the address and individual outputs.
Step 6
Configure the Mapping
Assign direction, brightness and function buttons.
Avoid unsuitable purchases and damage
Common Function-Decoder Mistakes
Confusing Locomotive and Function Decoders
A dedicated function decoder does not control a traction motor.
Checking Only the Number of Outputs
The output type and current rating are equally important.
Connecting an LED Without a Series Resistor
This can damage both the LED and the decoder.
Loading a Logic-Level Output Directly
It normally requires an additional amplifier circuit.
Leaving a Coupler Permanently Activated
The coil and decoder can overheat.
Choosing a Connector by Pin Count Alone
The standard and electrical pin assignment must also match.
25 decoders for coaches, control cars and special models
Suitable Function Decoders for All Gauges
The selection includes compact vehicle decoders, versions with standardised interfaces, flexible wired models and robust large-scale decoders.
Gauges N, TT and Small H0 Vehicles
Micro decoders, Next18, NEM 651 and compact lighting controllers.
Next18 Multiprotocol
ESU 59118 LokPilot 5 Fx micro
Compact lighting and function control.
View Product →
Next18 DCC
ESU 59128 LokPilot 5 Fx micro
Dedicated DCC version with several outputs.
View Product →
Micro NEM 652
ESU 59120 LokPilot 5 Fx micro
Compact eight-pin version for DCC.
View Product →
Micro Multiprotocol
ESU 59110 LokPilot 5 Fx micro
For DCC, Motorola and Selectrix.
View Product →
PIKO Next18
PIKO 56518 PSD XP 5.1 F
For coaches and lighting circuit boards.
View Product →
Mini Lighting Decoder
PIKO 46212
For selected N- and TT-gauge vehicles.
View Product →
TT NEM 651
Tillig 66031
Plug-in decoder for suitable TT-gauge vehicles.
View Product →
Mini with Wires
Uhlenbrock 73700
For lighting, flashing and time-controlled effects.
View Product →Gauges H0 and 0: Control Cars and Numerous Outputs
NEM 652, PluX22, 21MTC and vehicle-specific connections.
NEM 652
ESU 59210 LokPilot 5 Fx
Multiprotocol version with a wiring harness.
View Product →
PluX22 Multiprotocol
ESU 59212 LokPilot 5 Fx
Numerous outputs for modern control cars.
View Product →
PluX22 DCC
ESU 59222 LokPilot 5 Fx
DCC version with extensive function mapping.
View Product →
21MTC Multiprotocol
ESU 59219 LokPilot 5 Fx
Ten outputs for demanding vehicles.
View Product →
21MTC DCC
ESU 59229 LokPilot 5 Fx
For control cars and function models.
View Product →
PIKO Plug-In System
PIKO 56514 PSD XP 5.1 F
For compatible PIKO control-car circuit boards.
View Product →
Capacitor Connection
Uhlenbrock 76700
For buffered lighting and special functions.
View Product →
Six Outputs
Uhlenbrock 76800
Switching, dimming and flashing inside the vehicle.
View Product →Universal Wired, LED and Servo Versions
Flexible decoders for coach lighting, special functions and custom conversions.
Basic Without Wires
Tams FD-R Basic.3
Four outputs and one switching input.
View Product →
Basic with Wires
Tams FD-R Basic.3
Prewired version for conversions.
View Product →
Extended Without Wires
Tams FD-R Extended 2
Numerous switching and connection options.
View Product →
Extended with Wires
Tams FD-R Extended 2
For lighting, servos and special functions.
View Product →
Extended PluX12
Tams FD-R Extended 2
Five outputs and servo options.
View Product →
LED Without Wires
Tams FD-LED
For LED strips and coach lighting.
View Product →
LED with Wires
Tams FD-LED
Prewired coach-lighting controller.
View Product →Gauge G and Large-Scale Railways
High-capacity decoders for lighting and effects in large vehicles.
Refine the selection and prepare the installation
Suitable Categories and Guides
Answers before ordering and connection
Frequently Asked Questions about Choosing Function Decoders
What is a function decoder used for?
It is used for headlights, tail lights, interior lighting, couplers and other switchable functions inside vehicles.
Can a function decoder control a motor?
A dedicated function decoder normally does not contain a regulated motor output.
How many outputs do I need?
Every independently switchable lighting group or function normally requires its own output.
What is an amplified output?
It can switch a suitable electrical consumer directly, provided that the permitted current is not exceeded.
What is a logic-level output?
It provides a control signal and frequently requires an external amplifier.
Do LEDs require a series resistor?
Yes, unless the vehicle circuit board or decoder already provides suitable current limiting.
Can a digital coupler be connected?
Yes, when the output current and time-limited uncoupling mode are suitable for the coupler.
What is the benefit of a capacitor or energy-storage connection?
It can bridge brief interruptions in electrical contact and reduce flickering lights.
Are Next18 and PluX interchangeable?
No. The connector shape, installation orientation and electrical pin assignment are different.
Can a DCC function decoder be used with Märklin?
Yes, when the Märklin command station being used can transmit DCC.
What is the difference from a switching decoder?
A function decoder is normally installed inside a vehicle, while a switching decoder is generally installed in a stationary position on the layout.
When is professional installation advisable?
Professional conversion is advisable when the circuit board is unknown, currents are high, space is extremely limited or the vehicle is valuable.
Selection Principle
This page classifies function decoders by vehicle, interface, outputs, current rating, protocol and gauge.
Update Date
Content status: 17 July 2026. Check the manufacturer instructions and circuit-board pin assignment before making any connections.
Function Decoder Selected – Continue Planning the Digital Project
The main guide provides information about locomotive decoders, sound decoders, digital command stations, wiring, lighting and layout planning.