Updating the Bachmann Class 66 family of locomotives


Freightliner Class 66

GBRF Class 66

EWS Class 66/0

The Class 66 locomotive is still the most prolific freight motive power in the UK. There is little doubt that Bachmann's unit is the best OO gauge model of this ubiquitous locomotive currently available. However, Bachmann have chosen to include only a subset of the real world running lights and their speaker mounting arrangements can be improved upon. This web page collects together my most successful lighting and sound modifications.


Bachmann's Class 66:

Despite the lighting shortfall, the Bachmann design is a solid performer, with a heavy chassis and all-wheel drive providing good adhesion weight and load hauling performance, while all wheel pick-ups provide reliable electrical contact with all but the dirtiest of track. The on-board 21 pin DCC decoder connector greatly simplifies access to all available decoder outputs. These 66s all use a simple "common positive" lighting wiring scheme, which is straightforward to adapt for DCC based enhancements.

Bachmann have produced several variations on the Class 66 theme, but unlike the real Class 66 locomotives, none of these models incorporate a working night headlight or lower forward marker lights. I've used different detailed solutions to remedy this situation depending on the Class 66 variant concerned.

The latest Bachmann Class 66 units provide a reduced volume 20x40mm speaker enclosure, bolted to the top of the cast chassis block, directly below the cooler group fan output vent. However, in my experience, improved sound quality can be achieved using a very different location for the speaker.  



Lighting Update Summary

Gaining access to the lighting PCBs

Details for lighting updates on all three major sub-types

Sound System Summary

Further dismantling to access the fuel tank



Motor capacitor removal

Fitting a speaker in the fuel tank

Decoder recommendations

Circuit configurations

Circuit implementation



Colas Class 66

Lighting Update Summary:

A weak point of the Bachmann design is the much simplified running light arrangements provided in the original models. However, thanks to the availability of suitable LED components from specialist suppliers, the missing lower marker lights and night headlights can be fitted by enthusiasts with a steady hand and the right tools.

Indeed solder pads are provided by Bachmann on their lighting PCB, to accommodate a night headlight LED with its supply connection and outer lens. So the main challenge is the provision of the lower front marker lights:

Early Class 66/0 locomotives, used by EWS and now DB Schenker, have old style lower lighting modules which include small rectangular marker lights in the outboard position. In their Class 66/0 models, Bachmann have chosen to paint in non functional imitations of the marker light lenses. These are the most difficult to convincingly replace with working LEDs due to their small size and exposed location.


The next group of Class 66 lighting arrangements correspond to the introduction of dual function LED technology combined marker lights / rear lights to the real locomotives, combined with  large diameter headlight lenses. These are the easiest lights to improve.



Finally comes the most recent Class 66 light housings. e.g. 66731. These have smaller headlights and in their original condition, the Bachmann model lights exhibit a rather odd form of "tunnel vision", which can be improved by omitting the PCB frame support moulding and moving the PCB forward, immediately behind the lighting lenses.


Some proven techniques for lighting upgrades are illustrated in more detail below.



Dismantling the Bachmann model to gain access to the lighting parts.

First get together a few small containers or parts bags, ready to collect the screws and other small items, ready for re-assembly. Make sketches and/or take a series photos as you go, to make sure you have a record to remind you what fits where and which way around the various parts need to be during re-construction. You are unlikely to remember everything, so please record the key details!

The first step is to undo the 4 screws fixing the chassis to the upper body shell. (A zero point pozidrive screwdriver is the ideal tool.)


The screws don't always drop right out of their holes, so be prepared to catch them later in the process if you don't collect all 4 immediately.

Next the trickiest part of the exercise when dealing with a new model: Releasing the clips holding the upper body shell to the cab:

As shown in the photo, at each end, there are 2 side clips and one central end clip. My technique is to rest the unit upside down on a soft surface, carefully insert my thumbnails between the upper body side and the chassis, adjacent to the two side clips at one end and attempt to separate top from bottom, releasing the end clip in the process. This process often works better at one end or the other, so a bit of patience and a few attempts may be necessary. As the end clip becomes worn, the process becomes easier.


  Remove the flying lead connectors from their sockets on the main PCB, to separate the upper body shell.


Check which end has the driver and then ease off the two cab mouldings (Lever carefully with a flat screwdriver.)


Remove the small screw that holds each lighting frame moulding & PCB to the chassis baseplate.


 Carefully withdraw each lighting assembly from the chassis baseplate for attention.


Frame moulding

The PCB assembly can be pulled away from the rear of the frame moulding, ready for attention:



Adding The Missing Running Lights:


1) Adding a night headlight:

Solder pads are provided to fit a white 0603 sized LED to serve as a night headlight.


Make sure you get the polarity correct as this LED shares the day headlight positive connection.

A spare solder pad is provided on the rear of the PCB for the negative LED wire.

A series resistor is needed and some circuit modifications are required to integrate the new headlight with the DCC decoder.



The Technique For Fitting The Lower Marker Lights Depends On The Class 66 Variant:


2) Adding Marker lights for an early Class 66/0:

The original Bachmann marker lights are non-functional painted rectangles.......

A Class 66/0 model clamped in a modelling vice


Using a drill, craft knife and needle files, rectangular holes are carved into the lighting modules

where the original painted rectangles were located. Tiny holes are drilled upwards leading

from the holes into the bodywork, to exit behind the front face of the upper body front.


Pre-wired "Nanolight" LEDs by DCC Concepts (sourced from Digitrains) are glued in the apertures with their thin

enamel wire leads, routed through the holes into the locomotive interior.

NB: check the LEDs are the same way up, as they are not quite symmetrical when illuminated.

When the glue is dry, any collateral damage can be made good with a little filler and matt black paint.

The LEDs are connected via series resistors to the updated locomotive DCC circuit.

Note: The real rectangular marker lights use bulb technology and have yellow tint to the light output. If white LEDs have been used, this colour can be achieved by applying a thin film of yellow water colour paint over the LED front. 


3) Adding Marker lights for a later Class 66, fitted with dual rear/marker lights and large headlights:







The technique that I've found most successful for simulating the dual function rear and marker light installations is to paint the inside of the rear light cavity in the lighting frame moulding white. The lighting PCB is also carefully painted white around the rear light LED behind the rear light cavities. A white "Nanolight" LED is then glued to the top of the rear light cavity in the lighting frame. (Wires fed through small holes in the frame top.) When the marker light LEDs are illuminated, the white light bounces off the white painted cavity walls and reflects off the white paint on the PCB, to give a diffuse white glow through lens. When the rear lights are in use instead, they work normally, providing a simple way to produce a dual function rear and marker light in the model.


Showing the white paint applied to the lighting PCB.


Showing the marker lights on. The intensity above needs to be somewhat reduced by increasing the series resistors.

The LEDs are connected via the series resistors to the updated locomotive DCC circuit.


4) Adding Marker lights for the most recent Class 66 types.

The Light housings for the latest variants of the Class 66 seem somewhat deeper from front to back than their predecessors.... In my sole example, GBRF number 66731, in its original state, both day headlight and rear lights looked rather odd when viewed from any angle except from directly ahead. The effect was to darken the periphery of the lens face in what seemed to me to be a very non-prototypical way. After a number of experiments, I finally resorted to removing the lighting frame moulding completely and moving the lighting PCB right up to the rear of the lighting lenses. The lighting PCBs are held in place with Blu-Tack, leaving plenty of room to mount series resistors in the space directly behind the lighting PCB.

Showing the concept (before final refinements shown below.)


This required a new way to mount the marker light LEDs, in the absence of the frame cavity. The rear of the lenses had a lip that extended well below the level of the rear light LEDs, so I mounted the marker light LEDs on the lighting PCB, directly below the rear light LEDs, beaming directly at the extended rear lens lip.

Showing the extended lower rear lens lip.


The white marker "Nanolight" LEDs are glued to the PCB horizontally, below the rear light LEDs,

using a thin insulating base made from 0.2mm plasticard (to ensure no shorts to the original tracks).

The positive leads are trimmed and tinned then carefully soldered to the positive end of the adjacent headlight LEDs.

The negative marker LED leads are routed over the top of the PCB to individual series resistors.

Note also the plasticard fences glued but not yet painted black.


The absence of the frame also resulted in light leaking between the rear lights and the headlight lenses. This was stopped by gluing small black painted plasticard fences to the PCB between the rear lights and the headlights and by over-filling the small gap between the rear of the lenses with Blu-Tack.

Blu Tack squeezed between the adjacent lens rears.


Plasticard fences painted with opaque black enamel paint.

The marker light series resistors are isolated from the other resistors soldered to the PCB rear

by a sheet of thin plasticard, to which the resistors will be glued.


Blu Tack is also used to reduce light leakage from the top of the PCB assembly.


Sound System Summary:

I have updated models with both LokSound V4 and Zimo MX644D sound decoder hardware. Using Legomanbiffo V4 and Paul Chetter Zimo based sound projects. Both give excellent results and have similar speaker requirements. Zimo has many more function outputs and more user accessible programming options, while (in my opinion) LokSound V4 has a better designed function mapping arrangement, even if an additional function decoder may be needed to deal with more complex lighting control combinations. The 66 hardware upgrades are usually designed for specifically LokSound V4 or specifically Zimo decoders. This is because of different buffer amplifier requirements when more than 4 function outputs are in use on the V4.

Bif's LokSound V4 sound projects typically have a good level of peripheral sounds, combined with an effective largely automated driving system, which works very well. On my Zimo equipped 66s, I've just started to use Paul Chetter's latest Class 66 sound project, which uses his latest Zimo drive system, which he calls "Protodrive". This gives the user a lot of control, including a brake key which when combined with the high default CV4 setting, gives a realistic feel for the momentum of 126 tonnes of diesel locomotive, continuing to roll with the engine shut down. Separate braking action via key 2, is used to bring the locomotive to a halt. When hauling a maximum load train, key 7 can be used to wind up the engine notch settings independent of the speed control, so that the locomotive "unsticks" its train in a more realistic manner than typically found in fully automated drive systems. Thanks to some custom additions, I also have plenty of peripheral sounds to provide additional interest. 

Bachmann provide a 40x20mm speaker enclosure on their more recent 66s, mounted below the main roof fan vent. I've tried this fitting, but obtained better results by mounting the speaker, without an enclosure, sealed to the roof (using the locomotive body as an enclosure).  However I found that the fan vent grill was a source of intermittent rattling, which occasionally degraded the sound quality. So, I have finally settled upon a sealed fuel tank location, using an ESU 20x40mm type 50334 speaker, which faces downwards towards the rail track. This provides (to my ears) the best sound quality of the options I've tried.

Details on how to access the fuel tank and the speaker fit are provided below.


Continuing the dismantling process to gain access to the fuel tank for a speaker installation.

Dont forget: Use a few small containers or parts bags, to collect the screws and other small items, ready for re-assembly. Make sketches and/or take a series photos as you go, to make sure you have a record to remind you what fits where and which way around the various parts need to be during re-construction. You are unlikely to remember everything, so please record the key details!

Make a careful note of the connection points for the wires clipped to the tags on the sides of the main pcb.

Remove the clips and disconnect the wires. Carefully lever off the two plastic plates holding the wires in the groove forward of the motor.

Remove the small screw that holds each lighting frame assembly to the chassis baseplate.

Note which way around the main PCB is attached to the chassis block, then remove the two screws that hold the pcb in place.

Remove the main PCB and the lighting assemblies from the chassis.


Unscrew the Bachmann speaker enclosure from the chassis block.

Check which end each bogie is attached to (the bogies are not quite the same, so this matters!).

Remove the large screws that secure the bogies to the chassis and withdraw the bogies and their drive shafts, sliding the wheel contact wires through

the holes in the chassis block.


Check which way around the chassis block fits to the plastic chassis baseplate, then unscrew the four fixing screws.

Separate the chassis block and motor assembly from the plastic baseplate.

NB: You now have full access to all motor capacitors, so this is a good time to remove them for exclusive DCC operation. (see also section below.)

Check which way around the fuel tank fits to the chassis baseplate and remove the two sub-miniature screws holding the cable clamp in place.

Remove the two screws holding the fuel tank and battery box assembly in place and separate the assembly.


Undo the two screws that hold the ballast weight to the fuel tank and battery box plastics.

Carefully separate and remove the ballast weight.

Assuming that the underside switching function will be replaced by DCC control, remove the switch from the ballast weight by undoing the two retaining screws.

Using a hacksaw, cut the battery box section of the ballast weight along the red line and refit this to the inside of the battery box, using the original screw.


The dismantled Colas Class 66 with notes and bagged up screws and small parts.


Motor Capacitor removal:

If the locomotive is to be used exclusively in a DCC environment, the motor interference suppressor capacitors are best removed as they can disturb back emf drive systems operating at 40kHz. The three capacitors can be snipped off with cutters. However one of the capacitors restrains the motor contacts, preventing the lower lead from touching the cast chassis block. A suitable piece of plasticard can be glued to the chassis block adjacent to the problem lead beside the motor, to prevent an accidental short.

The lower capacitor is soldered at one end to the motor casing. To assist with the speaker construction below the motor, the remaining solder blob needs to be minimised in size. I found that slicing with a sturdy Stanley knife was a more realistic technique to remove the blob than attempting to melt the solder, with no risk of causing heat damage to the motor!




Fitting a speaker inside the fuel tank moulding:

The flat bottom of the fuel tank moulding is just wide enough to allow an ESU 50334 20x40mm speaker to be fitted without being immediately visible when the locomotive is on the track. However, the  electric motor protrudes below the top level of the tank, occupying some of the volume. In order to produce a sealed enclosure, some 3D plasticard construction is required to create a top plate for the fuel tank that incorporates a motor shaped intrusion.

The easy bit: cutting an exact size hole in the tank underside.


The speaker is sealed in position with an air tight bond.

The top plate is constructed to accommodate the bottom of the motor. The

plastic block is drilled to take the second fixing screw. All joints are sealed air tight.


Top view with new plate glued in place. (Note motor recess & fixing hole.)


All joints sealed, mounting strips glued in place and a coat of matt black paint applied.

The fixing screws have been put in place temporarily prior to re-assembly.


All exposed speaker metalwork also receives the matt black treatment.


The sound quality from this installation is the best I've achieved from a Class 66 update so far.


Decoder Recommendations:

A bit of history:

My first Class 66 updates were done several years ago, purely to add the missing running lights plus some strobing effects. (No sound.) I found at the time that the 21 pin standard 3 function Bachman DCC decoder (produced for Bachmann by the German ESU company) provided very smooth motor control, when compared to early TCS & Hornby decoders. However, this low cost decoder had only 3 function outputs, so I had to add a 4 output function decoder (TCS FL4) to obtain the lighting control I needed.

I believe that the original  Bachmann 21 pin decoder has now been superseded by a different type from another manufacturer. So the above option is probably no longer available.

Current Decoder recommendations:

Note: There are many other decoders available and some may be as good as these..... but I have had good experiences with all those described.

1) For smooth motor control and up to 6 function outputs, but no sound, I would recommend the 21 pin ESU LokPilot V4 decoder.

For sound equipped Class 66 units, I would take a look at:

2) The ESU LokSound V4 with a Legomanbiffo sound project for a largely automated (but very good) driving experience. (6 FOs available with comprehensive mapping options.) If more FOs are needed, a TCS FL4 (4 FOs, keys 0-12 only) or a LokPilot FX V4 (6 FOs, keys 0-28) function decoder in leaded configuration can be added. (FO = function output).


3) The Zimo MX644D with Paul Chetter's latest "Protodrive" sound project, if you prefer to have a more hands-on control of the driving process and more user access to the control CVs. (10 FOs available but with a slightly less comprehensive mapping arrangement than ESU.)  You are very unlikely to need an additional function decoder with a Zimo solution! I'm very impressed by Paul's latest Zimo driving enhancements and this is currently my preferred sound decoder.

Circuit configurations:

The circuit depends on the decoder function output arrangements and the controls to be applied to the finished lighting.

There are many possible arrangements, so I have just included my current sound equipped ESU and Zimo based solutions:

A "bare bones" LokSound V4 solution with day or night headlights activating diode fed markers and rears, but with rear light disabling for in-train use and a detonator flash LED for a bit of fun. Subdued cab light (instrument glow) is paralleled with the end 1 night headlight at the driver end only.

The more comprehensive Zimo solution permits independent day or night operation of the lighting at each end of the locomotive, supporting top and tail operation at either end of the train. plus switched driver's cab light, detonator flash LED and double strobe headlights at either end for yard movements.


1) LokSound V4 basic  (Without the speaker, this could also be used with a LokPilot V4 decoder for non-sound use)

The brown and pink function outputs, are Aux3 and Aux4 logic level outputs. The 2N7002 devices are N-channel MOSFETs, which invert

these outputs and provide an appropriate current handling level. The positive feed to the rear lamps is routed through the BSS84 which

is a P-channel MOSFET that can be switched on or off via the pink Aux4 function output, to enable or disable the rear lights under DCC control.



2) Zimo Double End with Headlight strobing facility:

The two PNP transistors at the top of the circuit diagram provide locomotive direction switched positive feeds to the headlights and marker lights, enabling separate control of the marker lights, which remain steady during headlight strobing.  (BSS84 MOSFETs can be used as an alternative to the PNP transistors if preferred.)


Circuit Implementation:

The circuit modifications are designed to work exclusively in a DCC environment. Once modified, the locomotives should not be subjected to Analogue track use.

Bachmann use a dual function circuit board, designed to operate on analogue 12V systems with a blanking plug fitted to the DCC socket or on DCC with a decoder fitted to the socket instead. Because I plan to use only DCC operation, I usually remove the main PCB components that are unnecessary for DCC operation. In the case of the Class 66 this includes a pair of large parallel 470 ohm surface mount resistors (which are replaced by a link) and the 4 large diodes. This has the effect of increasing the voltage applied to both original and new lighting LEDs and their series resistors. Consequently, I invariably fit my own choice of series resistor for both old and new lights, to achieve the lighting intensity I'm looking for. The circuit configuration is also likely to be different to Bachmann's original arrangement, so the original main board series resistors are also usually removed. To provide convenient anchor points for the new lighting cabling, I now isolate the 4 outer tabs at both ends of the main PCB, leaving only the central tab, which remains at common positive for ESU circuits. (Although even this is now also isolated on the latest Zimo implementations.)

The main PCB before surgery:

The board underside before track cutting commences, to isolate the outer solder tags at the ends of the board:

Typical appearance of the main PCB part way through modifications

Where a 21pin connector facility is available from the decoder, but the pin is not tracked on to the PCB e.g. Aux3 and Aux4, I use thin enamel coated wire off cuts from the "Nanolight" pre-wired LEDs and carefully solder these to the appropriate PCB solder pad for the pin concerned.

The new LED series resistors & other parts are mainly bonded to insulating plasticard substrates glued to the cast chassis block.


For YouTube video of 66731 (Earlier Digitrains Zimo) on the test track: Click here

For YouTube video of 66745 (Bif LokSound V4) on the test track: Click here


Supplier website links:


Rails of Sheffield    Normal sources for Bachmann locomotives
Hattons of Liverpool
DC Kits, D&E Video    Source for Legomanbiffo sound project equipped LokSound V4 decoders
soundsloco@btinternet.com    Email address to contact Paul Chetter if interested in obtaining Zimo decoder re-blows to incorporate his sound projects.

   Paul also produces occasional newsletter emails, with information concerning new Zimo sound project issues, contact him if you would like these sent to you.

Digitrains    The DCC Concepts Nanolight LEDs and ESU speakers are sourced from here. Digitrains also have a good range of Zimo decoders & sound projects
DCC Supplies    Knowledgeable and helpful suppliers of all things DCC
Amazon    An unlikely but often effective source for electronics components (although some parts take a while to arrive from China!)
Rapid Electronics of Colchester    A good reasonably priced source for electronic components.
RS Components    A good UK distributer of electronics components (eg MOSFETS) However, they may make a surcharge for small orders.




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