sd40-2 athearn lighting issue

Discussion in 'DCC & Electronics' started by jaijef, Oct 7, 2007.

  1. jaijef

    jaijef New Member

    have an Athearn Sd40-2 that I wired for DCC using a Digitrax DH163 decoder and the athearn wiring harness from Digitrax. I have only one problem now.
    I also wired in a 12v headlight and used a 22 Ohm resistor.
    However when I run the locomotive forward with the light on F8 the locomotive goes at top speed. When I push F8, the locomotive works properly in both directions.
    With the light on the brake does not work and the throttle can be set at 0 and the locomotive still goes forward.
    I have made sure the white wire from the decoder has the resistor attached to it inline with the lightbulb.
    The blue wire is wired directly to the lightbulb.

    Any suggestions to fix this problem would be appreciated.
  2. woodone

    woodone Member

    I am not sure if it will make any differance or not, the blue wire is the hot wire- the white provides the ground. I would try the resistor on the blue wire and see if it would change?
  3. Gary S.

    Gary S. Senior Member

    It sounds like somewhere, the blue wire is making contact with one of the motor wires, whether this is in the decoder, the plugin connector, or elsewhere. It is possible that the decoder could have a solder bridge across two leads, even from the factory. All this shuldn't be too hard to track down.

    The first check to perform is this: Do you have another decoder? Swap it out and see if the problem still exists. If this fixes the problem, then obviously the other decoder is the problem.

    If this doesn't fix it, then check all wiring very carefully, make sure there are no little strands sticking out and touching something they shuldn't be.
  4. jaijef

    jaijef New Member

    re:sd40-2 dcc lighting

    thank u all for the replies.
    I will check to see which it is.
    thank u again
  5. Robert Miner II

    Robert Miner II New Member

    SP GP40X lighting

    Okay, I'm about at wits end trying to figure out how to wire and make the top cab light on my Athearn GP40x work. I was told to go into the small hole on the circuit board behind the green wire using a 470ohm 1/4 watt resistor and one wire from each of the two bulbs while leaving the other two hooked up to thier original location. Is this right and if it is how do I get them to come on! I'm getting all sort of conflicting information on CV's to set to get the mars lights to operate. HELP!!!wall1
  6. PWRR-2207

    PWRR-2207 Rogue Islander

    What decoder are you using? I am pretty sure someone here (possibly me) has one and either has all the EPROM addresses or has got their MARS lights working....
  7. Robert Miner II

    Robert Miner II New Member

    I'm using a NCE D13SJR Decoder with 9 Pin jack.:thumb:
  8. PWRR-2207

    PWRR-2207 Rogue Islander

    Decoding the decoder...

    Ah-ha, now I understand the confusion. Since you were told to use a 470 ohm ½ watt surface mount resistor in the hole by the green wire on the decoder, I am going to assume that the light you are trying to activate is a 1.5 volt incandescent bulb with 30 milliamps of current running on a 16 volt track. (Assumption made on data taken from )

    You will need to set CV122 = 9 and verify that CV35 = 4 (factory default). As for wiring the “MARS” bulb, the blue wire from “Light Common” on the decoder should connect to the bulb and the green wire from “Output 3” on the decoder is the second wire to connect to the bulb to complete the circuit. This wiring and CV setting will cause the light to activate when the engine is set to run forward.

    If you want a second “MARS” light aft, you will need another resistor on “Output 4” that has a violet wire and set CV123 = 10 so the bulb activates when the engine is set to run in reverse, plus set CV35 = 12 so both “Output 3” and “Output 4” are controlled by “Function 1” (F1).

    (Part of the confusion about the CV’s may be because you can also set the lights to be on all the time by setting the registers CV122 and/or CV123 = 8. Plus, you can choose not to tie the “Output(s)” control to Function 1 (F1) by setting CV35 = 0 if you used the other “Output (3 or 4)” for “Ditch Lights”…)
  9. Robert Miner II

    Robert Miner II New Member

    Well I gave up on the GP40X Mars light, I think I was doing more harm then good. :eek: The SD45T-2 is next on the block using the same type decoder so I'll give it a whirl next weekend. :thumb: I surely appreciate the quick response and the advice. It will not be lost on the tunnel motors that I'll be working on over the next few weeks. I'll shoot you a line once I have been succesfull and am off of cloud nine over my newest feat in DCC (with much help from you). Thanks again and HAPPY RAILROADING! :wave:
  10. green_elite_cab

    green_elite_cab Keep It Moving!

    you will never get a digitrax decoder to work. They simply can't use headlights. the yellow and white wires go nowhere. I've been trying to get the dang things to work on all sorts of my locomotives, and the headlights NEVER turn on.
  11. Gary S.

    Gary S. Senior Member

    I've got several digitrax decoders in Athearn and Atlas locos and haven't had any trouble with lights. Now, several days ago, I did seem to have a problem where one of the decoders was losing its programmed address. I can't swear it was the decoder, maybe I did something wrong while programming. Overall, I've been happy with them.
  12. green_elite_cab

    green_elite_cab Keep It Moving!

    I think i need someone to look at my locomotives. I wire everything as it should be, yet it still never works.
  13. Robert Miner II

    Robert Miner II New Member

    Hope you had a great turkey day. I followed your advice on my sd45t-2 and the lights work like a champ. I went the same way on the sd40t-2 and different story. Now I have constant on lower headlights even when I switch over to reverse they stay on, and instead of "F1" turning on the mars light I hit "F2" and I get a burst of the lights being on the upper forward headlights for as long as I hold "F2". What the heck???? I hope you can bail me out on this one. Thanks, -Bob
    wall1 :curse: :confused: wall1
  14. Brian Greenough

    Brian Greenough New Member

    HI - I'm also having problems iwth a new DIgitrax DH165AO decoder i've installed in the Genesis F3a - it simply doesnt want to know about the forward lights. Does anyone have any suggestions?
  15. green_elite_cab

    green_elite_cab Keep It Moving!

    You have to be careful. If your headlights are rated higher, they will be dim. the DH165AO is good for those athearn headlights, (which are 1.5 volt bulbs) but not anything else really, unless you sever a particular connection (that i suggest you don't do because you might bust something else) that doubles the power, but it hardly seems to be enough.

    just totally abandon Digitrax decoders. they are never good investments. ever.

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