I have just purchased my first digitrax decoder. It is for an Athean GP50 locomotive. The decoder is a DH123AT. I can’t figure all the wiring from the directions because it isn’t specific enough. I requires a white wire connection to the forward light. Where exactly on the forward light? It also requires a black wire connection to the headlight post at front of frame. I am not sure of that location either. The rest I have figured out. I would like to get it up and running so I just don’t have analog locomotives running.
If I’m remembering the colors right.
You’ll have a BLUE and a WHITE wire going to the front headlight. If you’re using a standard 12v lightbulb, it doesn’t matter which wire gets attached to which lead. LEDs On tho other hand, are picky of which way you wire them. I don’t know that way (sorry).
As for the second part of your question → I believe the black and red wires are the track pickup wires. Red goes to the right side (of forward motion, relative to the engineer’s seat) pickups, and black to the left. As far as why you’d be wiring it to a headlight pickup, I don’t know.
I don’t have any Athearns with that harness handy so this is from memory:
The DH123AT harness is set up to provide half-wave current to the front light to reduce the bulb’s current draw and brightness. One side of the bulb (I forget which) will be grounded to the frame by way of that front post; the white wire goes to the other bulb contact. After you remove that long strip that clips on top of the motor and goes from truck to truck it will be more evident where the white wire goes. Just be sure it doesn’t come in contact with the other side of the bulb (grounded to the frame) or you WILL burn up the decoder.
As for the black wire, connect it anywhere to the frame side of that headlight post. Some folks drill and tap a small hole and attach the black wire directly to the frame, but I generally just solder it to the headlight post.
HTH,
Steve
Solder the white wire to the headlight post and the blue wire to the center contact of the bulb. That one can be a real pain!
For the default install the blue wire will not be connected to anything. The black wire connects to the light post that is riveted to the frame. The white wire connects to the position on the light where the big clip across the top of the motor used to connect to. Be sure to follow the instructions about the layer of tape under the motor to prevent the bottom brush clip from touching the frame.
–Randy
Just a FYI…the LONG lead (+) to the LED goes to the BLUE wire (+) and the resistor can go on either LED lead. You will need a resistor for every LED though.
David
The black wire will have a metal clip on it. This goes right to the metal post that comes up from the frame and attaches to the light. As for the other light wires, take the large metal bar off the top of the motor and you will have a copper strip that will want to drop and touch the drivetrain. The white wire will also have a clip but that clip will not fit on the post unless you fold the copper band over once or twice to make it thicker. Yellow is for the reverse light. Blue is the lighting common. The red wires attach to the posts that comes up from the trucks and you must put the clips on both trucks. Remember to isolate the motor from the chassis or you will burn the decoder up. Orange wire on the bottom of the motor and the grey wire on the top. Tuck the green and purple wires away they are for other functions. If I remember right you dont need to use the blue wire, the light will just be running on half wave power if you dont and full wave power if you do. There is a guide in the book DCC made Easy from Kalmbach that goes through the steps one at a time.
I found the link I was looking for last night that has a How-to on putting the decoder in an Athearn SD45. The steps are the same for what you are doing. This guy goes a little further with the lighting, you can copy his job or experiment on your own in that department or just hook up the stock cab light.
http://tcsdcc.com/decoderpics/Athearn%20SD45/athearn_sd45.htm
Good luck with the install.