Socket Shape
Two Parallel Rows of Contacts
The vehicle circuit board has a narrow two-row female header with eight intended positions in each row.
NEM 658, pin assignment and decoder selection explained clearly
PluX16 Interface Explained: Choose the Right Decoder
PluX16 connects the motor, track pickups, driving lights, auxiliary functions, loudspeaker and energy storage through a compact two-row connector. This guide explains how to identify PluX16 and choose a suitable locomotive or sound decoder for N, TT and H0.
Modern plug-in connection for compact digital technology
What Does PluX16 According to NEM 658 Mean?
PluX16 belongs to the PluX family defined by NEM 658. The vehicle circuit board has a two-row female header, while the pins are located on the underside of the decoder. The pitch is 1.27 millimetres.
The name PluX16 describes 16 intended positions. The numbering runs from pin 3 to pin 18. Pin 11 is omitted and the corresponding socket position is blocked. This index position is intended to prevent the decoder from being inserted rotated or offset.
PluX16 carries the track voltage, motor connections, front and rear lighting, two amplified auxiliary functions, two logic-level connections, loudspeaker connections, decoder positive, decoder negative and a connection for an energy-storage capacitor.
The interface does not determine the digital protocol. A PluX16 decoder may support DCC only or several formats such as DCC, Motorola, Selectrix and mfx-compatible registration. The protocol, motor current and decoder dimensions remain separate selection criteria.
Check the connector shape and index position carefully
How Do I Identify a PluX16 Interface?
Indexing
Position 11 Is Blocked
The missing pin position forms the mechanical key and identifies the correct installation orientation.
Decoder Side
The Pins Are Under the Board
Unlike 21MTC, the PluX decoder itself carries the pin header.
Blanking Plug
Analogue Operation Before Conversion
In an analogue vehicle, a blanking plug connects the track, motor and lighting.
Labelling
Check the Packaging and Instructions
Vehicles with a factory-installed interface should be identified as PluX16 or PluX16-S.
Dimensions
The Connector Alone Is Not Enough
The length, width, height and component clearance above the locomotive circuit board must also suit the decoder.
Do not identify the interface by contact count alone:
Compare the missing index position, the location of the pins and the
available installation space with the vehicle instructions.
Motor, track signal, lighting, sound and energy storage
Pin Assignment of the PluX16 Interface
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Why Does PluX16 Start with Pin 3?
The PluX family uses a common numbering system. PluX22 covers positions 1 to 22, while PluX16 uses the central range from 3 to 18. This allows vehicle circuit boards and decoders within the family to be coordinated mechanically in some applications.
Pin 11 is not an electrical connection. The missing pin and blocked socket position form the reverse-polarity protection. A decoder must nevertheless never be forced into the interface.
| Pin | Designation | Function | Output Type | Check |
|---|---|---|---|---|
| 3 | GPIO_A / AUX8 | Train-bus clock or logic function | Logic level | Do not connect high-current loads directly |
| 4 | GPIO_B / AUX9 | Train-bus data or logic function | Logic level | Suitable for control signals and bus functions |
| 5 | GND | Decoder negative after the rectifier | Power supply | Relevant to energy storage and electronics |
| 6 | Cap+ | Positive connection for an energy-storage capacitor | Power supply | Use only according to the decoder instructions |
| 7 | F0 Forward | Front headlight | Amplified | Observe the decoder output-current rating |
| 8 | Motor Positive | First motor connection | Motor output stage | Measure motor current under load |
| 9 | U+ | Decoder positive after the rectifier | Power supply | Do not connect to a separately generated vehicle positive |
| 10 | Motor Negative | Second motor connection | Motor output stage | The motor must be isolated from the track pickups |
| 11 | Index | Mechanical keying | No connection | The position remains blocked |
| 12 | Right-Hand Track Pickup | Right rail connection | Track signal | Connected to motor positive in analogue operation |
| 13 | F0 Reverse | Rear headlight | Amplified | Check the direction-dependent assignment |
| 14 | Left-Hand Track Pickup | Left rail connection | Track signal | Connected to motor negative in analogue operation |
| 15 | Loudspeaker A | First loudspeaker connection | Audio | Observe the sound decoder's impedance specification |
| 16 | AUX1 | First auxiliary function | Amplified | Often used for a separately controlled tail light |
| 17 | Loudspeaker B | Second loudspeaker connection | Audio | Do not connect to the vehicle ground |
| 18 | AUX2 | Second auxiliary function | Amplified | Check the function assignment of the locomotive circuit board |
Distinguish contact capacity from decoder output:
NEM 658 specifies a maximum of 1 A for the connector contacts. The
permitted motor and function current of a specific decoder may be
considerably lower and must be taken from its data sheet.
Classifying PluX12, PluX16, PluX16-S and PluX22
Which PluX Version Fits the Vehicle?
| Version | Positions | Standard Installation Space | Typical Use | Special Feature |
|---|---|---|---|---|
| PluX12 | 12 | 20 × 11 × 4.2 mm | Compact locomotive decoders | No longer recommended for new designs |
| PluX16 | 16 | 20 × 11 × 4.2 mm | Locomotive, function and compact sound decoders | Loudspeaker, energy-storage and logic connections provided |
| PluX16-S | 16 | 28/30 × 16 × 6 mm | Larger sound decoders | No longer recommended for new applications |
| PluX22 | 22 | 30/35 × 16 × 6 mm | Feature-rich H0 locomotives | Additional amplified outputs available |
| 21MTC | 22 positions with 21 contacts | Separate standard dimensions | H0 locomotive, sound and function decoders | The pins are located on the vehicle circuit board |
Do not assume partial compatibility:
A smaller or larger PluX decoder may only be used when the socket,
unused holes, mechanical installation space and electrical function
assignment of the vehicle permit it.
Three details for an initial decoder recommendation
Which PluX16 Decoder Fits My Locomotive?
The interface is only one of several purchasing criteria
How to Choose the Correct PluX16 Decoder
Motor Current
Choose Continuous Output with a Reserve
Measure the current consumption under load. Small N-gauge decoders are not automatically suitable for older H0 motors.
Dimensions
Check 20 × 11 × 4.2 mm
The standard size is a maximum value. Body supports and the flywheel may reduce the space that can actually be used.
Functions
Distinguish Amplified and Logic Outputs
AUX1 and AUX2 are amplified. GPIO connections provide logic levels only and frequently require suitable circuitry on the vehicle board.
Sound
Plan the Loudspeaker and Project Together
Check the loudspeaker impedance, sound enclosure, sound project and available installation space.
Protocol
Match the Command Station and Decoder
DCC, Motorola, Selectrix and mfx-compatible registration are decoder features, not properties of the interface.
Locomotive Model
Check the Model-Specific Assignment
With prepared sound solutions, the locomotive class, production series, vehicle circuit board and loudspeaker mounting must match.
Compact technology for small and medium-sized vehicles
PluX16 Applications by Gauge
Gauge Z
The interface is rare because of its physical size. Wired or specialist decoders usually require less space.
Check
Decoder height and motor current.
Gauge N
Newer, larger N-gauge locomotives may have PluX16. Micro and nano decoders are particularly suitable.
Check
Clearance above the locomotive circuit board.
Gauge TT
PluX16 is widely used in modern diesel and electric locomotives and provides sufficient contacts for sound and lighting.
Check
Distinguish clearly between PluX16 and PluX22.
Gauges H0 and H0e
Compact H0 locomotives, shunting locomotives and railcars use PluX16, while larger models often have PluX22.
Check
Motor output and range of functions.
Gauge 0
PluX16 is possible but rare. The motor output may exceed the capacity of a micro decoder.
Check
Starting current and heat dissipation.
Gauges 1 and G
High-capacity decoders with wires, screw terminals or PluG are generally more suitable for large-scale railways.
Check
Multiple motors and auxiliary loads.
Insert the decoder with the power off and without mechanical pressure
Install a PluX16 Decoder in Six Steps
Step 1
Test the Locomotive in Analogue Operation
The motor, gearbox, current pickup and lighting must operate reliably.
Step 2
Open the Body
Release screws, clips and wires according to the vehicle instructions.
Step 3
Document the Interface
Photograph the socket, index position, blanking plug and installation space.
Step 4
Remove the Blanking Plug
Pull it straight out of the socket without tilting it.
Step 5
Align the Decoder
Check the index position and insert the decoder evenly.
Step 6
Use the Programming Track
Read the address and test the motor, lighting and auxiliary functions individually.
Sound installation:
Loudspeaker wires must not be connected to the vehicle ground or
track connections. The impedance and power rating must comply with
the sound decoder instructions.
Avoid confusion and electrical damage
Common Mistakes with PluX16
Treating PluX16 and PluX16-S as Identical
The sound version may require considerably more installation space.
Forcing the Decoder into the Socket
Bent pins can damage the socket, decoder and vehicle circuit board.
Connecting a Load Directly to a Logic Output
GPIO connections are not normal amplified lighting outputs.
Using PluX22 Without Checking
Not every vehicle circuit board has unused holes and sufficient installation space.
Not Measuring the Motor Current
Older H0 motors in particular may overload a micro decoder.
Choosing the Sound Project by Locomotive Class Alone
The circuit board, production series and loudspeaker may differ despite the same locomotive designation.
21 locomotive and sound decoders organised by application
Suitable PluX16 Decoders for N, TT and H0
The selection includes compact locomotive decoders, universal blank sound decoders and model-specific sound decoders. Always check the vehicle series, installation dimensions and function assignment before ordering.
Gauges N and TT: Compact PluX16 Decoders
Micro and nano versions for small locomotives and TT sound projects.
Micro Multiprotocol
ESU 59814 LokPilot 5 micro
Compact locomotive decoder for small vehicles.
View Product →
Micro DCC
ESU 59824 LokPilot 5 micro
Compact DCC-only version with additional function outputs.
View Product →
Nano Sound
ESU 58914 LokSound 5 Nano
Blank decoder supplied with a compact loudspeaker.
View Product →
TT Class 130
PIKO 46542 SmartDecoder XP S
Model-specific sound with a suitable loudspeaker.
View Product →
TT V 60
PIKO 46544 SmartDecoder XP S
Shunting-locomotive sound with a suitable loudspeaker.
View Product →Gauge H0: PluX16 Locomotive Decoders Without Sound
Multiprotocol and DCC versions for motor control, lighting and auxiliary functions.
PIKO Multiprotocol
PIKO 56502 PSD XP 5.1
Modern motor control and extensive function mapping.
View Product →
Roco Feedback
Roco 10895
Updateable locomotive decoder with feedback.
View Product →
IntelliDrive 2
Uhlenbrock 74150
Compact decoder with extended function mapping.
View Product →
1.1 A Decoder
Kühn 82760 T65-16
Locomotive decoder with SUSI and six function outputs.
View Product →Universal PluX16 Sound Decoders
Blank decoders and universal sound solutions for N, TT and H0.
LokSound Micro
ESU 58814 LokSound 5 micro
Multiprotocol sound decoder with a loudspeaker.
View Product →
ZIMO Sound
ZIMO MS450P16
High-capacity H0 sound decoder.
View Product →
Roco Sound
Roco 10893
Updateable sound solution with feedback.
View Product →
PIKO Blank Decoder
PIKO 56508 PSD XP 5.1 S
Blank multiprotocol sound version.
View Product →Model-Specific Sound Decoders for Gauge H0
Prepared sound projects for specific locomotive classes. Some versions combine PluX16 or PluX16-S with an additional eight-pin connection.
Class 130
PIKO 56540
Sound project for the large DR diesel locomotive.
View Product →
V 200
PIKO 56541
Diesel-locomotive sound with a suitable loudspeaker.
View Product →
Class 119
PIKO 56547
Model-specific sound solution with a connection adapter.
View Product →
Class 118
PIKO 56557
Prepared sound project for suitable Class 118 models.
View Product →
TRAXX
PIKO 56611
Model-specific sound for suitable TRAXX locomotives.
View Product →
G 1700
PIKO 56612
Diesel-locomotive sound for suitable G 1700 models.
View Product →
Desiro
PIKO 56581
Railcar sound for suitable Desiro models.
View Product →
BB 67400
PIKO 56625
Diesel rail-vehicle sound with a loudspeaker.
View Product →
Explore decoder selection and digitisation in greater depth
Suitable Product Categories and Guides
Answers before ordering and installing a decoder
Frequently Asked Questions about the PluX16 Interface
What does PluX16 mean?
PluX16 is a two-row decoder interface according to NEM 658. It carries the motor, track, lighting, sound and auxiliary-function connections.
How many electrical contacts does PluX16 have?
The version covers 16 positions from pin 3 to pin 18. Pin 11 is omitted as the mechanical index position and is not connected electrically.
Can a PluX16 decoder be inserted the wrong way round?
The blocked index position is intended to prevent this. The decoder must nevertheless only be inserted with the power off, straight and without force.
What is the difference between PluX16 and PluX16-S?
PluX16-S provides for a larger sound-decoder installation space. The current standard no longer recommends this version for new applications.
Can a PluX12 decoder be used in a PluX16 socket?
This may be possible with a standards-compliant arrangement. However, the functions of the additional PluX16 positions will then not be available.
Can a PluX22 decoder be used in a PluX16 socket?
Only when unused socket positions, the mechanical space and the vehicle circuit board permit it. Not all decoder functions may be usable.
Is PluX16 suitable for sound?
Yes. The interface includes two loudspeaker contacts. The sound project, loudspeaker impedance and installation space must also be suitable.
Which lighting outputs does PluX16 provide?
The front and rear lights as well as AUX1 and AUX2 are intended as amplified outputs. Other connections may provide logic levels.
Can an energy-storage module be connected?
PluX16 provides decoder positive, decoder negative and Cap+. The specific energy-storage circuit must comply with the decoder instructions.
Is PluX16 the same as 21MTC?
No. With PluX, the pins are located on the decoder. With 21MTC, they are normally located on the vehicle circuit board.
Which gauges use PluX16?
The interface is used particularly in N, TT, H0e and compact H0 locomotives. The gauge alone is not reliable proof of the interface fitted.
When is professional installation advisable?
Professional installation is advisable when contacts are bent, the circuit-board assignment is unknown, the motor current is high, the model is valuable or a demanding sound conversion is planned.
Technical Basis
The contact assignment, index position, dimensions and installation guidance from the 2025 edition of NEM 658 were considered.
Update Date
Content status: 17 July 2026. The current vehicle and decoder instructions remain decisive before installation.
PluX16 Identified – Continue Planning the Decoder and Digital Project
The main guide covers locomotive decoders, sound decoders, digital command stations, protocols, digitisation and layout planning.