Sountraxx DCC Hardwire help

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HO Scale MILW

HO Scale MILW

A Normal, Regular, Train Fan
Hey all, I recently purchased two Soundtraxx MC2H104OP mobile decoders to install in a couple Athearn RTR Sd40-2s that I have. One of the units had an 8-pin plug, and the decoder went in and works fine, however the other unit is too old and required the decoder to be hardwired. I cut the 8-pin plug off and hardwired the locomotive based on the wiring designations (Black left rail, Red right rail, Grey motor left, Orange motor right), yet the locomotive will not work. I tested the connections, and the connections to the motor work (the motor spins), but the ones picking up power from the track do not (the power is going through the decoder in this test). Does anyone know why this might be? Did I wire it incorrectly?
(edit, the red wires were just to extend the decoder wires, as they were not long enough)
IMG_20250302_171915.jpg
 
HO Scale MILW said:
Hey all, I recently purchased two Soundtraxx MC2H104OP mobile decoders to install in a couple Athearn RTR Sd40-2s that I have. One of the units had an 8-pin plug, and the decoder went in and works fine, however the other unit is too old and required the decoder to be hardwired. I cut the 8-pin plug off and hardwired the locomotive based on the wiring designations (Black left rail, Red right rail, Grey motor left, Orange motor right), yet the locomotive will not work. I tested the connections, and the connections to the motor work (the motor spins), but the ones picking up power from the track do not (the power is going through the decoder in this test). Does anyone know why this might be? Did I wire it incorrectly?
(edit, the red wires were just to extend the decoder wires, as they were not long enough)
View attachment 213172
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There's probably an issue with the left rail pickup. Make sure the area of the frame that contacts the truck is making good contact, and make sure you run a wire between the front and rear truck for reliable right rail pickup.
 
Sadly I don't think that's the issue. I checked the joints again and all of them seem secure, when I removed the left and right rail pickups and put wires from a DC controller up to the decoder wires themselves the motor still didn't turn, thinking it might be the decoder but not sure? Possibly the soldering iron damaged it? It's a dual mode decoder so I don't think testing it with DC is the issue...
 


HO Scale MILW said:
Sadly I don't think that's the issue. I checked the joints again and all of them seem secure, when I removed the left and right rail pickups and put wires from a DC controller up to the decoder wires themselves the motor still didn't turn, thinking it might be the decoder but not sure? Possibly the soldering iron damaged it? It's a dual mode decoder so I don't think testing it with DC is the issue...
Click to expand...
What address are you using? What address did it have? Have you reset it?
 
Currently I have a DC layout, but I plan to get an NCE powercab within the next few months, so the address should still be 3.
 
You need to get some kind of DCC system before you go any further. Attempting to hardwire a decoder without having a way to test it and make sure it works is a recipe for disaster.
 
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