Updating the Bachmann Class 70  lighting to include operation with no headlights but all 3 marker lights on.



The RMweb forum includes regular entries in the "prototype discussion" section by a senior Colas driver, who often posts photos of his locomotives, including many of the Colas Class 70 units. These frequently illustrate Class 70 locos working in the yard or, stationary, while awaiting permission to proceed, with the headlight off. In this state, all 3 forward marker lights are on. I am advised that (unlike a Class 60) the driver has to manually switch on the headlights before proceeding. However, when the headlight activates, the marker light adjacent to the active headlight is automatically switched off.

This seemed like a good subject for an interesting mini-project, which I shall extend to also provide optional automatic switching (as per Class 60) and an idea for a super-shunter lighting mode.

NB: This webpage gathers together elements of my approach to the project. It illustrates just one of many different solutions to this problem and may not include sufficient detail to easily copy without building up your own understanding of what is involved!


Illustrating the Class 70 lighting options with photos obtained from the RMweb forum, with many thanks to "Big Jim" for permission to use them!

                  In the yard with all three forward markers illuminated

Showing the dual function lower marker lights in rear light mode                             

Day running lights with right hand headlight on and the right hand marker light off.

Night running lights with left hand headlight on and the left hand marker light off.


Bachmann's original lighting:

The Bachmann original lighting scheme does not include the night headlights and the original marker lights have significantly higher intensity than the day headlights.

These problems are addressed and fixed in the earlier Class 70 DCC Update pages. So the starting point for this project is a set of bright day and night headlights, supported by much lower intensity marker lights.

A recent TV documentary showed detachable orange strobe warning lights being placed on the lamp irons of container train locos as they entered the container depot. In response to this, I have already fitted home brew versions of these strobes on the 70, and these will be retained.


Project Outline:

My sound equipped 70 currently has a LokSound V4 with a Bif sound project on-board. The plan is to update the loco as well as I can, while retaining this decoder, with its 6 function outputs. However, I will also consider ways to make future enhancements that would expand the lighting capability to also include independently controllable cab light and a detonator flash LED, controlled by an additional function decoder. If a Zimo MX644D had been used, instead of the Bif LokSound, all the additional functionality could be accommodated without the need for an additional function decoder.... If/when a comparable Protodrive Class 70 sound project becomes available from Paul Chetter in the future, I may decide to take that route instead.

First steps are to modify the hardware to enable separate day or night headlight operation and to make each headlight automatically shut down its adjacent marker LED, when the headlight is active.

Next, the new lighting needs to be incorporated into the DCC function mapping, with appropriate control keys assigned. 



The Proposed Circuit diagram:

Mods to the lighting PCBs:

The original lighting circuit is as follows:


A few changes are needed:

This time, I plan to fit the additional series resistors at the main Board end of the interconnecting cables.  First the lighting PCBs need to be restored to their original configuration by deleting the link added in the original lighting update and bridging the track cut applied at the same time..... Then the links and track cuts shown above need to be implemented. I've also replaced the original stiff cables between the lighting boards and the main board with more flexible types.

Lighting PCBs with the key tracks indicated in green:

NB: The lower picture is a photo shopped mirror image to make it easier to see how the vias link the top & bottom tracks!

Black rectangles on the upper photo show where original resistors have been removed; red line = track cut; blue line = new link.

Yellow triangle shows connection points for the now remotely mounted day headlight LED leads.


Main Board modifications: 

The peripheral components are mounted using two plasticard substrates.  Common positive, Ground and all FO lines are derived from the main board tracks. All lighting PCB interconnect cables now go directly to the new substrates and not via the original main board tracking. The main board tracks are modified to implement the new circuit & enable the new substrates etc to interface with the two 4 pin sockets to the upper body shell. The upper body shell night headlights and amber strobe wiring will now route via a new 6 way connector.

My Main Board mods. NB I'm sure there are better ways to implement the circuit around the original board!


The modified loco: 


Chassis assembly with cabling taped down.



Proposed LokSound FO & mapping arrangements: 


Select Action Direction & Key Condition, F Key,  FO(s) Mapping line
Double or single end operation markers & rear lights Set light engine running lights with no H/L (yard mode) Fwd F20 Fwd, F(20), White  (H/L FO) 26
Rev F20 Rev, F(20), Yellow (R/L FO) 1
Set train haul running lights with no H/L (yard mode) Fwd only F21 Fwd, F(21), White  (H/L FO), Brown (Aux 3) 27


Day or Night Headlights....


Manual or automatic activation only when moving.

Set day headlights (manual) Any F22 F(22), green (Aux 1) 28
Set day headlights (automatic) Any F23 Moving only, F(23), green (Aux 1) 29
Set night headlights (manual) Any F24 F(24), purple (Aux 2) 30
Set night headlights (automatic) Any F25 Moving only, F(25) purple (Aux 2) 31


Remove original lighting programming from keys 0, 11, 13 & 14:

Mapping line  Alpha values CV32 Actual CV values
5 CVA=0,  CVK=0 2 321=0, 330=0
6 CVA=0,  CVK=0 2 337=0, 346=0
17 CVA=0, CVD=0, CVK=0 3 257=0, 260=0, 266=0
18 CVA=0, CVD=0, CVK=0 3 273=0, 276=0, 282=0
19 CVA=0, CVD=0, CVK=0 3 289=0, 292=0, 298=0
20 CVA=0, CVE=0, CVK=0 3 305=0, 309=0, 313=0

Programming CVs for new lighting arrangements:

Mapping line Key  Alpha values CV32 Actual CV values
26 F20 > CVA=4, CVF=16, CVK=1 3 401=4,  406=16,  410=1
1 F20 < CVA=8, CVF=16, CVK=2 2 257=8,  262=16,  266=2
27 F21 > CVA=4, CVF=64, CVK=17 3 417=4,  422=64,  426=17
28 F22 <> CVG=1, CVK=4 3 439=1,  442=4, 
29 F23 > CVA=1, CVG=4, CVK=4 3 449=1,  455=4,  458=4
30 F24 <> CVG=16, CVK=8 3 471=16,  474=8
31 F25 <> CVA=1, CVG=16, CVK=8 3 481=1,  487=64, 490=8


Fixing the shortcomings:

Unfortunately, the LokSound Aux 4 logic output is now permanently on and no longer responds to key control (may have accidentally shorted the underside of the decoder to a pad on the board, which perhaps explains the fault.) This leaves me without a means to control the warning strobes mounted on the lamp brackets at each end of the loco. Also, with only 5 working FOs, the cab light is in the on state, unless the headlights are activated, without any external control. Bif's sound project includes an impressive triple detonator element and it would be good to be able to add a white LED near the front wheel to synchronize with this.......for all these reasons, I'm going to add a spare TCS FL4 function decoder, to resolve these shortcomings.

Proposed supporting TCS FL4 function decoder mapping:

Action CV number Value
Set pink output to double strobe fwd & rev 54 37
Set green output to continuous forward only 51 0
Set purple output to continuos forward only 52 0
Assign pink output to key zero 40 3
Assign green output to key 11 37 64
Assign purple output to key 12 38 128
Set alternate CVs to zero 35, 36, 42 0


Adding a speculative flashing super-shunter mode. (This is just for fun):

When freight locos are used to shunt in the yard, those equipped with separate white marker lights and rear lights (e.g. Class 60) typically display all markers and rear lights at both ends while working the yard, however, more recent locos typically have dual function light fittings that can be used either as forward white marker lights or as red rear lights. Clearly a different approach would be required to create an equivalent effect. One idea is to alternately flash the red and white functionality:

Apply alternate flashing of white marker lights and red rear rear lights by using H/L FO and R/L FO using config 2, with a phase shift to the R/L FO........

Mapping line Key  Alpha values CV32 Actual CV values
32 F26 > CVH=1, CVL=16+32 3 504=1,  507=48
    H/L FO no phase shift 0 355=12, 359=0
    R/L FO phase shifted 0 363=12, 367=1
    flash rate 0 112=20

Works well.....

Updated Circuit Diagram, now including the FL4 Function Decoder:

The cab light positive supply is also shifted to common positive so that it can be used with the controller set to either direction.


FL4 decoder mounted on the front substrate


Active Button Sound Slot Assignments (& Lighting Controls): 



Function list     (Lighting options highlighted)

F0 Yard Warning Strobe lights on.
F1 Sound On/Off and engine start/stop.
F2 Playable High Note Horn.
F3 Playable Low Note Horn.
F4 Buffer Clash/Buffering up when moving slowly.
F5 Air Release (Air Dump).
F6 Drivers door slamming.  
F7 Compressor Startup.  
F8 Dynamic Braking Fan Enable. 
F9 Flange/Wheel Squeal Enable.
F10 Dispatcher's whistle.
F11 Detonator flash LED (When fitted).
F12 Cab light Disable.
F14 Notch-up.
F15 Notch-down.
F17 General Electric Skipfire Idle Enable.
F18 Triple Detonators.
F19 Set zero momentum (for test purposes only).
F20 Yard mode running lights Light Engine.  OR:
F21 Yard mode running lights train haul. (forward only)
F22 Day headlight on.             OR:
F23 Day headlight to automatic (only on when moving).
F24 Night headlight on.            OR:
F25 Night headlight to automatic (only on when moving).
OR None of (F20-F25) and instead:
F26 Alternate rears & markers Super shunter mode.



Lighting Options in action:


Yard Mode

Rear lights


These two lighting patterns are alternated every half second for the speculative Super Shunter Mode


Day running lights



Night running lights



"On" phase of double strobe warning lamps


Supplier website links:


Rails of Sheffield    The Freightliner Class 70 unit 70006 was purchased from this excellent web supplier.
Rapid Electronics    Excellent source of sensibly priced electronic components.
DC Kits - D&E Videos    The source for Legomanbiffo sound equipped LokSound V4 decoders
Maplin    Convenient local source for resistors and transistors, although the prices reflect that convenience.


Photos of the real class 70s were taken by "Big Jim" & copied with his permission (Thanks Jim!) from the RMweb forum site.   The photos of the model were taken hand held on the kitchen worktop.


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