sd40-2 athearn lighting issue

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.
Sincerely
Jaijef
 

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?
 

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.
 

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.
 

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?
 

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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