Since it's an E7A, you only need a front headlight, right? So, you can wire the front LED to the blue and yellow wires, and then reverse the FOR and FOF bits in the CVs. Setting CV 33 to 2 and CV 34 to 1 should accomplish this.
It takes an iron man to play with a toy iron horse.
What your testing is showing is that the white is somehow positive. Yellow is workign as it should, and so is the blue. The only way for the white to be a positive would be a major defect somewhere, as even if the controlling transistor on the decoder were burned out it still only connects to ground, it would either always be open or be permanently fused to ground. So there is a serious fault here that is probbaly not goign to be easily corrected without sending the deocder back to Digitrax.
Did the wires ever come off and you resoldered them? White is next to blue, so if there is a blob of solder spanning the space between the pins of the connector on the decoder board, that would cause this effect. This may be a remnent from manufacturing, and they way circuit boards are automatically assembled.
--Randy
Modeling the Reading Railroad in the 1950's
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The blue wire should be positive. The white and yellow wires should be negative. If they are not, the decoder is wired incorrectly, or is bad internally.
Do you have a meter? The right thing to do would be to check the voltages. If you don't have a meter, well, the right thing to do is get one.
Examine the decoder. If you see a small dark spot burned through the blue plastic, that's an indication that part of the decoder has burned out. It could be a birth defect in the decoder, or the result of mis-wiring.
Do you have the capability to post pictures, alloboard? A close up of the decoder and the wires running to your LED in the same pic would be helpful...
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
I have a Digitrax SDH164D installed in my Proto 2000 E7A diesel locomotive. I think that the blue (+common) and white (F0F) wires coming off my Digitrax SDH164D are both negative while the yellow (F0R)is positive. I believe that the blue (+common) wire is supposed to be positive and the white is negative and the yellow positive. I found this problem out because I am trying to install an LED headlight and the white and blue wires do not work only yellow and white or yellow and blue when the locomotive is in reverse. How can I fix or reverse this issue?