# Installing DCC in a Bachmann Large Scale 4-4-0



## mapper65 (Feb 15, 2009)

I'm trying to install a Digitrax DCC decoder in a Eureka & Palisade Large Scale 4-4-0. The Bachmann drawing shows the stock DC wiring and they include a drawing for wiring in a DCC decoder. The DCC drawing shows the wiring for a Lenz 1835 decoder. I connnected the track power and motor leads to my Digitrax decoder and the thing runs fine. What I can't get to work is the lighting.
I printed out the manual for the Lenz decoder to compare with the Digitrax decoder and as far as connecting up the head light and firebox lights, it seems like that information is not correct. They show A,C & D on the Lenz decoder being connected to the black wire and terminals 3&4 on the Bachmann factory board. If you compare that to the Lenz manual, it looks like they are wiring the forward lighting output to the black lead and C&D on the Lenz decoder appear to be function outputs. That kind of makes sense but they don't show the blue + wire being used. In my past experience, the blue wire needs to be used to complete the circuit. Nothing is shown on the Bachman drawing as to what terminals 3&4 do. The black wire on the Bachman drawing looks like it goes to the "-" side of the headlight.
Does anyone know the correct wiring for the lighting. I could easily cut the headlight wire and wire it directly to the decoder with a resistor but the firebox lighting would be a little more tricky since you can barely get to those wires due to them being on the side of the board that is still pretty much in the boiler when you slide the board out. I have to believe that since Bachmann shows the loco wired to a decoder that the lights can work properly with a decoder. I think something got lost in the translation of the drawing. I'd like to not have to cut the firebox light wires and hard wire to the decoder if possible. Any help would be greatly appriciated. Thanks


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## Greg Elmassian (Jan 3, 2008)

Most locos are wired for negative ground, and as you know, in DCC, you really need positive common between lights. 

So, if several lights are wired to a common, everything is normally backwards for DCC, which makes for more changes for you. 

I'd just rewire the headlight directly, and then likewise wire the flicker power to the negative and the common (positive) on the Digitrax. I don't remember if the Digitrax brings this out. If not, then you need to get it from the full wave bridge minus on the decoder. 

Regards, Greg


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## mapper65 (Feb 15, 2009)

The Lenz drawing shows them connecting each of the 3 functions to points of the decoder to points in the loco which would be correct as far as DCC goes but I thought there needs to be some reference of the common + (blue wire) from the decoder to the loco for those outputs to turn anything on. Right now those outputs would be floating since the circuit is not complete until the path goes through the blue wire of the decoder which is not shown on the drawing.


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## George Schreyer (Jan 16, 2009)

I don't know anything about that particular loco, but Bachmann often supplies their own "blue" wire in the form of a 9 to 12 volt bus. The decoder can still switch those to it's own internal ground and it will work. 

Look at my Heisler and Railtruck pages, they may have some similarities to the 4-4-0 

http://www.girr.org/girr/tips/tips9/heisler_tips.html 
http://www.girr.org/girr/tips/tips8/bachmann_railtruck_tips.html


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## mapper65 (Feb 15, 2009)

Posted By mapper65 on 15 Apr 2010 08:30 PM
I ended up getting it working tonight. Here is the proper wiring and I didn't need to remove the Bachmann factory board or cut any wires or wire the lighting directly to the decoder. I used a Digitrax DG583S decoder. I used a separate Tsunami 1000 Light Steam in the tender for sound which is pretty straight forward so in this example I'm only going to explain how to wire the decoder in the loco for the motor and lighting. I'm going to try and save others a whole lot of time. I have read where people doing similar locomotives have either removed their factory board or have cut their fire box lights and have wired everything including the headlight direct to the decoder. That will work but I have to believe that this is a whole lot easier and this entire installation of the motor and lighting decoder should take you about an hour, possibly less. I suggest having the DC & DCC schematics that came with the loco handy for reference. George was right that Bachmann is supplying the + common on the Bachmann board. I also found out that you can't go by the Lenz wire colors that they show on the DCC schematic. 
Here goes... 
Motor 
Remove the red & black wires from terminal block 7 & 8 on the Bachmann Factory board. Connect the black wire to screw terminal 1 on the decoder and connect the red wire to screw terminal 8 on the decoder. These are the track power connections on the decoder. In the box with the locomotive they gave you two short wires, one red, one black. If you don't have those, make two wires up about 4 inches in length and preferably black and red. Connect the black wire to terminal 8 on the Bachmann factory board and connect the red to terminal 7 on the Bachmann factory board. Now take the other end of the black wire and connect it to pin 2 on the decoder. Take the other end of the red wire and connect it to pin 7 on the decoder. These wires power the motor. 
Lighting 
There should be an orange yellow jumper wire and a white jumper wire on the Bachmann factory board between terminals 4&5 and terminals 3&6. Remove those wires, you're not going to need them. On the Bachmann factory board there will be a black wire on terminal 2. Remove this wire from terminal 2 and connect it to your decoders Forward Light Output. On the Digitrax decoder, this is the solid white wire which is 5th from the left on the wiring harness. I soldered mine and used shrink tubing to shield the solder joint. Next, on the decoder's wiring harness, wire Function Output 5 (white/green stripe wire) to terminal 3 on the Bachmann factory board. Then, take Function Output 6 (white/blue stripe wire) on the decoder and connect it to terminal 4 on the Bachmann factory board. Output 5 will control the firebox lights and I have no idea what Function output 6 does but Bachmann show this connected. You may chose not to connect it. 
I would suggest testing this before your put it all back together. Be sure that the decoder board or the Bachmann factory board are not touching anything that can short them out. When I tested mine I found that in order for the headlight to light be on in the forward direction, the switch inside the smoke box needed to be set for Large Scale. If it was set for NMRA then the light was on only in reverse. You could also correct this by changing a CV value or wiring to the reverse light function output. It's your call. 
Be sure you put something between the bottom of the Digitrax decoder and the top of the Bachmann factory board before pushing them back into the boiler in order to keep the two from shorting out. 
Also, the smoke unit will still work by turning it on and off in the smoke box. I took a voltage reading on the LM7812 voltage regulator and everything looks good. I had around 15 volts DC on the input and 12 volts on the output. 
That's it.


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## mapper65 (Feb 15, 2009)

PLEASE NOTE: After re-reading my post, the first sentence under "Lighting" should read. "There should be an yellow jumper wire and a white jumper wire on the Bachmann factory board between terminals 4&5 and terminals 3&6." I typed orange instead of yellow.


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