I just started installing the digitrax decoders into my athearn blue box engines today. The installation has gone pretty well but I am questioning what to do with the “blue” wire. Is this supposed to be parralled into all the lights? I am adding a rear light right now and more than likely ditch lights in the future. I can understand the rear needing a common but shouldn’t the front already have that with the post going out the trucks? I appreciate any help.
The blue wire is common to both lights. White is for the front light, yellow for the rear and blue goes to both. This gives you the ability to configure the lights as whatever you want. Steady, Mars, gyralight, etc. Don’t use any connection to the lights that comes from the trucks or the frame. This won’t allow you to configure the lights and you may blow the decoder.
does this mean I have to disassemble my front head light post? Is the white, green, purple, then basically your negative side and your blue wire gives you your +voltage to the light? what output voltage is given out from these functions?
Yes, you have to disassemble the Athearn stock headlight and use a different bulb or LED because the Athearn “fire in the cab” bulb is connected directly to the frame through the mounting bracket.
The blue decoder wire is the positive 12 Volt lead to all lights; white, yellow, and green are the negative leads that are the ‘function’ inputs to the decoder.
And don’t forget to put resistors with all bulbs or LEDs – a separate resistor for each.
And you must remove the motor from the frame so you can connect one of the decoder wires to the bottom brush contact strip and insulate the motor from the frame.
All of this information is contained in the Digitrax Mobile Decoder User Manual that can be downloaded from the Digitrax web site. It should also be contained in the instructions that come with every decoder.
You are correct that the white, yellow, green and purple wires are the “grounds” and the blue wire is the common positive. I’m not familiar with the light post construction but you will have to isolate the headlight so that it only gets power from the blue and white wires.
Joe
In all the Athearn BB locos I’ve converted the light post bracket in question is attached directly to the frame and holds the headlight bulb. A plastic clip on the back of the bracket holds a brass wiper clip that transfers power from the front truck to the center terminal of the bulb. Icut the bracket so only a half inch sticks up from the frame. That gives me a convenient place to attach the ground wire for the decoder and I don’t have to drill and tap a hole in the frame.
Ok, I am on the right track then. I just need to take apart the headlight and I should have it all set. The rest of the installation was nice and easy I just wasn’t sure about that front headlight approach. Do you guys have any suggestions on the size of bulbs or what you used to simulate a bracket to have the light mounted to? I was thinking a piece of plastic square tube glued to the frame. The two engines I am working on right now are a GT sd-40 and a NS c44-9w. I appreciate the replies, it has helped alot.
Actually you can use a connection from the truck or frame for the light. Decoders allow you to use either the left rail or right rail pickup instead of the blue wire for power to the lights. It is very important that you only use one or the other on each light, though. For example, on the front light one wire goes to the white wire and the other goes to EITHER the blue wire OR one of the rail pickups, but absolutely not to both at the same time. You also would still be able to configure the light, but it would be dimmer than it would if you used the blue wire.
Some decoders(such as ones with the 6 Pin NEM 651 Plug) don’t even have a blue common connection and depend on either the left or right rail pickup to supply ‘+’ power to the lights.