# NEW HERE! Question on replacing both trucks on DCC locomotives



## gcollins2021 (Apr 22, 2021)

Hello everyone! I just signed up for the forums and I hope my question is in the appropriate location.

I just replaced both trucks on my DCC locomotive because of some failed wiring and I ran into a snag after putting the train back on the track. When I put the loco on the track and try and power the rail (test track), the command station says there is a short. Now being new to DCC and all and out of model railroading for at least 20 years I know it's probably something stupid I'm doing.

First there were no instructions with the replacement trucks. I just put them in and plugged in the wire from the trucks into their proper plugs. I would think the decoder buddy plus would be properly configured so I never worried about the replacement. Bit as I said above, using both trucks and powering up I get a short indicator.

When I unplug one truck and try it again, it works just fine. I then switch the trucks and try it again and it works just fine. I'm thinking the wiring MUST be switched on one of the plugs because one truck is in what would be considered reverse polarity (I know there is no +/- rails) while the other is in the proper orientation. 

So I guess my question is, do I swap the red/black wires on one truck at the decoder buddy board? And if so, which would? Front truck or back truck?

If someone could give some tips, that would be great!

Thanks!

Glen


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## CTValleyRR (Jul 26, 2014)

Sounds like one of the trucks is installed backwards. Try just reversing one of them (don't change the orientation of the wires when you do).


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## gcollins2021 (Apr 22, 2021)

CTValleyRR said:


> Sounds like one of the trucks is installed backwards. Try just reversing one of them (don't change the orientation of the wires when you do).


Thanks for the reply. The trucks only go in one way since they have worm gears as part of the truck. I don't know if moving the front truck to the back and the back truck to the front would make a difference. I unfortunately don't have a continuity meter to test the connectivity and how they are at the plug going into the decoder. I just have to do right now and see what happens.


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## CTValleyRR (Jul 26, 2014)

No, it's a polarity issue: one of your trucks is providing left rail power to one pole of the motor, the other is providing right rail power to the same pole. Both trucks need to provide the same polarity of electricity to their end of the motor (or to the same input on the DCC decoder). Can you post a nice, clear, well-lit picture or two of the trucks and their wiring?


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## gcollins2021 (Apr 22, 2021)

CTValleyRR said:


> No, it's a polarity issue: one of your trucks is providing left rail power to one pole of the motor, the other is providing right rail power to the same pole. Both trucks need to provide the same polarity of electricity to their end of the motor (or to the same input on the DCC decoder). Can you post a nice, clear, well-lit picture or two of the trucks and their wiring?


Sure. There is not much to see as the wires for the truck power go into the truck themselves. I'll upload the decoder board and what is seeable for the trucks.

Decoder Board










Front Truck











Rear Truck










I tried swapping the connectors for the truck power. No luck there either. I'm thinking about taking one of the truck connectors and swapping the red/black but I wanted to check here 1st!

Thanks much for any assistance!

Glen


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## MichaelE (Mar 7, 2018)

I would try metering the connections first. If that is not possible then swapping wires in the connector would be my next step too.

If you don't have a multi-meter yet, now is a good time to get one.


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## mesenteria (Oct 29, 2015)

Is it possible you have one or more axles reversed?


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## J.Albert1949 (Feb 3, 2018)

Unplug one truck at a time from the controller board.
See if it will run with only one truck connection plugged in.
If that works, try with the OTHER ONE plugged in...

You haven't told us who the manufacturer of this engine is...?


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## DonR (Oct 18, 2012)

The wiring of a DCC locomotive is very simple.

The Red wire from the decoder goes to the 
RIGHT RAIL wheel pickups of BOTH TRUCKS.
The Black wire from the decoder goes to the 
LEFT RAIL wheel pickups of BOTH TRUCKS.
The two red wires are connected together, as are
the two black wires, and are the power input to
the decoder.

Don


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## Lemonhawk (Sep 24, 2013)

It's not apparent which side of the truck the red wire goes to. That's where an ohm meter might help. If you try each truck by itself and nothing shorts and it still works then it's likely that reversing the red and black going into one (only switch one) will fix things. If one of the trucks does not work, then at least you have isolated the problem and need to replace the truck.


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## gcollins2021 (Apr 22, 2021)

Hi everyone! Thank you ALL for your diagnostics tips! I was able to get ahold of the manufacture of the replacement trucks and I was told they manufacture the trucks generically. No front or rear just one way. So I was told (as I kind of suspected) to reverse one of the trucks wiring at the plug to resolve the issue. And it indeed did resolve the issue. It's running again!

Thanks again everyone!

Glen


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## CTValleyRR (Jul 26, 2014)

Glad you got it sorted out. As you just discovered, they may wire their trucks generically, but it makes a world of difference where the inputs end up!


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