How do I hard wire Hornby DCC decoders into a locomotive?

A lot of people ask us how to hard wire a DCC or TTS Sound decoder into a locomotive.  It could be that the locomotive pre-dates the ‘DCC ready’ plug and socket system, or that it was never fitted.  This can be quite common with 0-4-0 and 0-6-0 type trains.

Before you start, remember this guide is for Hornby DCC decoders including the R8249, and TTS Sound range.  So if you’re using a different manufacturers chip – please contact them for help first.



Step-by-step guide & wiring diagram

A simple wiring diagram has been provided by Hornby to help you make the connections in your locomotive.  It’s important to remember that you should take your time in doing this to avoid damage to the locomotive electrics, body and chassis.


Hornby DCC decoder wiring guide
Hornby DCC decoder wiring guide


We’ve also provided a brief step-by-step guide to help you:

  1. Remove the plug from the decoder chip.
  2. Locate the wires from the pick ups and remove from motor using a soldering iron.
  3. Solder the Black & Red wires from chip, one to each pick up wire.
  4. Solder the Grey & Orange wires to the motor contacts.
  5. Locate a suitable decoder position.
  6. Make sure all excess wires are bundled up so not to interfere with wheels, gears & valve gears.
  7. Test and programme loco to unit.
Important note: There should be no other connections from the pick ups to the motor and any bare wires need to be isolated to prevent short circuits.  Also, if the locomotive has lights, follow the colour diagram shown.




Quite often people experience issues running their train once they have fitted a DCC decoder.  Ensure you refer to the configuration information provided with both the decoder and your controller to get them talking to each other, and always use a section of ‘programming’ track.

Remember also that the DCC element may be more sensitive to dirty track and poor connections than when it was DC powered.  Ensure that the tracks, wheels and pickup points on your locomotive are as clean as possible.

Hornby Locomotive Decoder installation manual (R8249)

Hornby NMRA Compliant DCC Locomotive Decoder

Download the instruction manual



Replacement instructions for the Hornby standard DCC locomotive decoder (R8249).  Contains information on supported CV settings, connection information and more in English, Italiano, Français, Deutsch and Español.

The Hornby locomotive decoders may be used with all standard digital control equipment that conforms to the NMRA standards.

Note the normal running current carrying capacity of the Hornby Decoder is 500mA peaking at 1Amp shared with the Function outputs.  If this capacity is exceeded
the decoder will cut out.  The decoder must not touch any metal parts of the locomotive as this may cause a direct short and permanently damage the decoder.

Do not wrap the decoder in insulating tape as the decoder requires a cooling smooth air flow across it’s surface.  If air is restricted the decoder may over heat and be damaged.  As a precaution it is advised that any exposed metal surfaces that the decoder may come into contact with are covered with insulating tape, especially on the surface where the decoder is to be installed.

If there is no decoder housing for the decoder to be located into, the decoder can be fixed in position using double sided tape or pads.

Decoder equipped locomotives must not be operated using an overhead power supply or catenary system.

Before installing the Hornby Decoder make sure that the model runs efficiently in DC mode.  A poorly running locomotive will not be improved by adding a decoder.



Download the instruction manual