DCC conversion and Lighting update of the Bachmann Class 66/9  Heavy Freight Diesel Locomotive



This page provides a summary of the process adopted to incorporate DCC decoders and correctly operating external LED lighting in the Bachmann "late model" Class 66/9, OO gauge, heavy haul diesel locomotive (in Freightliner and DRS-Stobart Rail liveries).

Note that the smaller pictures can be enlarged by clicking on the image.


Scope of the project:

DCC control: The unit has a Bachmann 21 pin decoder socket built-in. The Bachmann 3 function decoder gives incredible low speed handling on this model. It is therefore the decoder of choice for motor drive. However an additional decoder with greater programmability is also required to provide full lighting control.

Lighting arrangements: The Bachmann model correctly incorporates the later style of Class 66 light fittings. However, only some of the lights operate. The main objective of this project is to model correct day and night operation of the lighting, using an additional TCS FL4 four function decoder to supplement the Bachmann decoder.

The Bachmann model is only fitted with operational right hand (daylight) headlights, so left hand (night running) headlights need to be added. The real, late model, Class 66/9 locomotives are fitted with a pair of dual function LED technology front marker lights / rear lights at each end. (The same light assembly is used as either a white marker light or as a red rear light). On the Bachmann model, these lights only operate as rear lights, so a means must be found to introduce an additional white light source that beams through the same lens. The top marker lights operate correctly but are much too bright. These need to be reduced in intensity. The rear lights can be disabled (when the loco is at the head of a freight train) by means of a mechanical switch on the underside of the model. This operation will also be controlled via the DCC controller.

On the real loco, daylight running uses all three forward marker lights plus the right hand headlight. Night running uses all three forward marker lights plus the left hand headlight. Both rear lights are used during day and night running if the loco is moving "light engine" i.e. without a train in tow. When towing a train, no rear lights are shown by the locomotive, but instead, a single rear facing, flashing red rear light is fitted to the rear wagon of the train. (To see a way to produce a realistic flashing rear warning light for DCC freight trains: click here).


Day running Lights

Rear Lights


Lighting Concept:

The Bachmann decoder provides a white wire output that is only active when the loco controller indicates forward and a yellow wire that is only active when the controller indicates reverse. These lines can be used to directly control the new marker lights and the rear lights.


Headlight control for day running or night running will be controlled by the new TCS FL4 decoder. To conserve 2 output functions for other tasks, it will be necessary to use transistor switching of the positive supply to the headlights, driven by the Bachmann decoder white and yellow wires, plus the FL4 green and purple wires on the negative side, to define which of the 4 headlights is active.  The diagram below shows how this should work.

In order to be able to enable/disable the rear lights from the controller, another transistor switch will be used in the positive supply to both sets of rear lights, controlled by the FL4 brown wire.  (See the block diagram below.)

Finally, making use of a double strobe effect available in the TCS decoder, the FL4 pink wire will enable all 4 headlights to be strobed as a hazard warning when running in the freight yards. Diodes will be used to isolate the pink wire from other control wires. (See the circuit diagram below.)



Circuit Diagram for the planned new lighting system: 

The Bachmann decoder provides directional white and yellow wire outputs that are used to power the marker and rear lights. The TCS FL4 decoder is used to power the headlights and to select day or night running lights. PNP transistor switches under the control of the Bachmann white and yellow wires, enable the head lights at the correct end of the loco. A third transistor switch, under the control of the FL4 decoder, switches the rear lights on or off. An additional hazard warning mode of headlight operation is also available using the FL4 decoder pink wire.  Additional resistors are fitted in series with the top marker lights and cab lights to reduce their brightness. The resistors in series with each LED control the current flowing through that LED. This determines the intensity of the light generated by the LED. The above values were established by experiment, for the LED types employed. Some adjustment may be required if different LED types are used.


Number 1 and Number 2 Locomotive End Definition:

The Class 66/9 units have a longer cab at one end compared to the other. The long cab end is regarded as the number 1 end of the locomotive.

Achieving Access to the locomotive:

First the upper body shell must be separated from the wheeled chassis unit.  This is a difficult operation, as the mouldings fit very tightly together. First, the 4 screws must be removed from the bottom of the loco, then the The lower edges of the sides need to be gently eased outwards at each cab end, to release the plastic clips at the side of each cab and on the front face of each cab.

                          Underside of loco                         


Screw hole close-up (Click on close-up picture to enlarge)


Upper Body Shell separated from Chassis, before disconnecting the two wiring plugs

(Note this loco already has an earlier less comprehensive lighting update fit.)


Showing the chassis clip locations


Showing the corresponding clip receptacles in the body shell


Access to the Lighting PCB Assemblies:

The inner cab moulding can be pulled upwards and separated from the chassis unit. Below the cab, the main lighting assembly, consisting of a surface mount PCB and a plastic support frame,  can be lifted clear of the chassis assembly.

Fitting the missing left hand headlights:

The right headlight and 2 rear light LEDs are mounted on the PCB. Copper pads are also provided for an 0603 sized left hand headlight. With some care, it is possible to solder a white SMD LED device to these pads, using a soldering iron with a small bit, tweezers and a fair bit of patience! The new LED has a common anode connection to the original headlight LED. The cathode connects to a spare solder pad on the rear of the PCB.


Inner Cab moulding removed


Lighting PCB frame eased upwards


Lighting PCB removed from frame

Rear view of original frame


How to add a front marker light capability to the rear lights?:

The first approach researched was the use of dual white/red SMD LEDs, but only leaded dual function LEDs could be found, which were (a) too big and (b) used "golden" white for the white light in place of the correct "pure" white.

So thoughts turned to an alternative idea of adding a separate white LED source that could share the rear light lens with the existing rear light LEDs.  Eventually, the penny dropped that there is room to accommodate small leaded LED devices between the inner cab moulding and the lighting PCB frame top.  Two holes were drilled through the frame top into the cavities below that housed the rear lights. Miniature white LEDs (sourced from Bromsgrove Models) were then placed so that the 1.6mm LED lens was inserted into the holes. The concept worked, but the white light was quite dull. Results improved dramatically when the inner surface of the lighting cavity in the frame was painted matt white, to improve reflections. This worked so well, all 4 cavities in both front and rear lighting PCB frames were painted white.

DCC Supplies sourced 1.8mm white LEDs were used for the marker lights on the Freightliner unit. These worked just as effectively.


Top view of lighting PCB frame showing new LED holes

Lighting PCB frame showing white painted cavities


Reducing unwanted "Light bleed" between the new LEDs:

Light from the LED bodies may be visible through the loco body mouldings and may couple into adjacent devices if fitted straight out of the bag, producing a very unrealistic effect. To prevent this, the LEDs are painted with gloss black modelling enamel, leaving just the output lens exposed. A white dot was then painted on the negative side of the LED body (shortest lead) before use, to avoid later wiring errors. Once the LED leads are trimmed, its easy to forget the polarity!   


Holding the new LEDs in place:

The new LEDs were held in place on the lighting PCB frame with temporary blobs of Blu Tack, while the wires were soldered. Holes were drilled through the inner cab moulding just above floor level and the LED connecting wires were passed through these and soldered to the LEDs. The frame and inner cab were then re-assembled and permanent pieces of Blu Tack were used to hold the LEDs firmly down on top of the frame.



Prototype with rear lights activated

Prototype with marker lights activated


Evolution of the decoder and control circuitry:

The use of two decoders with cross connected controls, via the external transistor switches was a "first" for me. The main concern was the voltage difference that might occur between the positive reference lines of each decoder. However, the potential difference turned out to be less than 0.1 V. However, the TCS decoder had to be indepenently programmed, before the links between the decoder control lines were made.  The Bachmann circuit external to the plug-in Bachmann decoder, did require some changes to be made, in particular, linking out the parallel pair of 470R resistors between all the loads and the positive reference line.

The final circuit diagram illustrated above is the result of a number of refinements with respect to the initial design.


Fitting the decoder and control circuitry:

Strips of double sided adhesive foam tape were placed over the available space on top of the cast metal block, on either side of the main PCB. (Taking care not to obstruct the fixing screw holes). The components were soldered together to form convenient circuit modules. The modules were then placed in appropriate positions on the adhesive foam tape pads.

The circuit modules were then wired up in line with the circuit diagram, except that the connections between the Bachmann decoder circuit and the TCS decoder circuit were left disconnected until the TCS FL4 decoder had been programmed. (These are marked with a red X on the circuit diagram).


Circuit placement on the Freightliner Class 66/9 chassis before wiring up


Circuits fully wired on the DRS / Stobart Rail Class 66/9 chassis


Programming the CVs:

Using the DCC controller (mine is a Bachmann Dynamis) the CV values were programmed into the TCS FL4 decoder (by direct connection of the controller output wires to the red and black leads of the FL4 decoder, with the Bachmann decoder completely isolated from the controller).

FL4 CV Purpose

FL4 CV Number





Green wire function  (rule 17 dim f&r)



Purple wire function (rule 17 dim f&r)



Brown wire function (full on f&r)



Pink wire function (x2 strobe f&r)






Green wire control button (2)



Purple wire control button (1)



Brown wire control button (9)



Brown wire control button (9)



Pink wire control button (6)






Dimming active (headlights)



Dim amount (headlights)



Dim all the time button (5)







The "rule 17" dimming option provided in the TCS decoders has been used, so that when the train is stationary, the headlights and marker lights are dimmed. As soon as the train is made to move, these lights come up to their normal intensity.


Final Decoder Connection:

Immediately after programming, the TCS decoder address was reset to that of the Bachmann decoder address.

The controller was then disconnected and the links (marked with a red X on the circuit diagram above) between the decoder outputs and the control transistor base circuits were soldered together. The TCS decoder was then connected in parallel to the Bachmann track connections.  Additional series resistors were fitted to the top marker light and cab light assemblies in the upper bodyshell to reduce the intensity of the LEDs involved.

The upper bodyshell was re-connected and re-attached to the chassis unit, leaving the locomotive ready for testing.

Yellow and White function wire plus rail track connection locations on the Bachmann PCB assembly

(click on the image to enlarge)

DRS / Stobart Rail upper body shell

Testing the Lights:

Button 0 should activate the marker lights in the forward end of the loco and with Button 9 also pressed, should activate the rear lights in the rear end. (Rear lights are switched off by leaving button 9 off.)

Button 2 activates the right hand (daylight running) headlight in the forward end of the loco, or alternatively, button 1 activates the left (night running) headlight and the cab lights.

With buttons 1 and 2 off, Button 6 should activate all 4 headlights in double strobe hazard warning mode for yard shunting operations.


Day running lights are OK stationary (buttons 0,2,9)

Freightliner moves & headlight goes full beam

Freightliner Rear lights work OK (buttons 0,2,9)


Freightliner Night running OK (0,1,9) and Stobart reverse OK (buttons 0,2,9)


Night running lights stopped are OK (buttons 0,1,9)


Also: Button 9 off, switches off the rear lights OK.

Buttons 0,9,6 provide front markers and rear lights plus double strobe on all 4 headlights

Conclusion: All working well!


The finished Class 66/9s (lights off)

Click here to jump to the Class 66/0 update page, which deals with additional modifications required for the earlier EWS Class 66 Locomotives

......and then there were three!  GBRf Class 66/9 with daylight running lights on.


Supplier website links:


Hattons of Liverpool    The Freightliner Class 66/9 unit above was purchased from this excellent supplier.
Model Junction    The Stobart Rail Class 66/9 unit above was purchased from this excellent shop in Bury St Edmunds.
Trains 4 U (Peterborough)    A good (almost local) source of Bachmann and Dapol product. They also stock TCS decoders and offer good technical advice.
Bromsgrove Models    Excellent source of DCC decoders and specialist LED devices for this type of project
DCC Supplies    DCC specialist supplier based in Worcestershire. Good prices on Tower LEDs and TCS decoders
TCS (Train Control Systems)    A U.S. company. My preferred DCC decoder family with good programming data and advice on their website.
Maplins    My usual source for resistors and transistors, with convenient local shops.


Photos of the real class 66 were taken at Skipton in June 2009.   The photos of the model were taken on the kitchen worktop, using a tripod at 200 ISO with available light from an illuminated magnifier.    


Click to move to Model Rail Index Page

Click to return to Duxford-Update