I used Digitrax DN142 decoders in these locos, simply because I had the decoders. A better choice would probably have been the cheaper DZ121 decoder. Decoder installation is really rather a waste on this loco since it is most definitely not a good performer. Probably the best choice for this loco would have been a DN121, which was much cheaper than both the DZ121 and DN142.
There's plenty of room for either, although I have a feeling that the DZ121 is narrower and will fit into the shell easier. The DN142 was a bit tight on width.
To remove the loco's shell, pry the sides open enough to release the two clips on each side of the chassis. (These clips are visible in the two unprototypical holes on each side of the shell, one just behind the cab and the other more or less above the front wheel of the rear truck.)
The loco has no rear light installed. If you want to install a rear light, you'll first have to pierce the light lens holes in the frame. I used a drill bit that's small enough to enter the blind light holes, and it pierced the holes easily when twirled between the fingers. For a lamp you'll need a lamp similar to the front one. (I've found that the little 12v lamps that are used to light up radio/VCR/TV controls work well, but it's probably best to get the proper lamp from your hobby shop or from LifeLike.)
Discard the rear ballast weight to make room for the decoder. (It's lead, in case you're into making your own sinkers for fishing. If you live in California, don't even touch it!) Remove the screw at the bottom of the fuel tank that holds the motor in place, carefully slip the drive shaft springs off the ends of the motor shafts with a small tool like a jeweller's screwdriver or even a pocketknife blade, and lift out the motor from it's seat in the plastic chassis.
Power pickup from the trucks are via two wires from each truck directly to the motor brush caps. The headlight's two wires are also connected to the brush caps. Since the motor is mounted in a plastic chassis and all electrical pickup is via these wire connections, there's no need for any modifications to the frame to isolate the motor. Simply unsolder the headlight's two wires and the truck pickup wires from the motor brushes, leave all four loose truck wires sticking out to the sides of the chassis to be out of your way, and you're ready to begin decoder installation.
Do the orange motor wire first. It goes to the bottom brush cap on the motor, and must be long enough to pass over the top of the motor and down the front past the drive shaft housing to the brush cap, with the decoder resting on top of the rear truck tower gearbox, and with the end of the decoder flush with the rear end of the gearbox. After soldering the orange wire to the motor, reinstall the motor in its seat and fasten it with the motor screw.
After doing this, it's a good idea to temporarily tape the decoder in place above the gearbox, because a decoder with up to eight more loose wires flapping around while you're working can become tiresome.
Next, connect the gray wire to the top motor brush. Connect the two wires from the left (fireman's) side of both trucks to the black decoder wire, and connect the two wires from the right (engineer's) side of both trucks to the red decoder wire. Make sure all connections are properly insulated, preferably by using heat shrink tubing.
Make sure that the truck wires will not interfere with wheel turning or with lateral truck movement. You'll see that there's a "path" for these four wires on the chassis, with four clips moulded as part of the frame on each side of the chassis to hold the wires in position, just ahead and to the rear of the motor cavity. Thread the wires along these paths and press them into these four clips to hold them in place and out of the way of the drive shaft springs.
Connect the white wire (and if you're using a DN142 decoder, violet wire as well) to one end of a small ballast resistor (20 to 40 ohms will do) and the other end of the resistor to one of the headlight wires. Connect the yellow (and green, if it's a DN142) wire to one of the rear light wires, also via a 20 to 40 ohm resistor. Then the blue wire gets connected to the second wires of both lamps. I let the rear lamp hang loose behind the rear gearbox and the decoder, but with the wires bent double so that the light bulb "stands" on its wires to get the light more or less in line with the light holes that I drilled in the frame.
If you used a DN142 decoder and connected the violet and white wires together, and the yellow and green together, it is possible to program directional blinky light functions of your choice to the F1 (green) and F2 (violet) leads. Then, with F0 off and F1 and F2 on, the loco will have the blinky lights of your choice, and when F0 is turned on (without having to turn off F1 and F2), the lights will be on steady. (On DT100 throttles F2, being intended for the horn if sound is used, is on only while pressed. To keep it latched on, press F2 and while holding it down, also press Run/Stop. Pressing F2 again will unlatch it again.)
Remember to triple check for shorts before taking the loco to the programming track. There must be no direct contact between the track and the motor. Make sure that all wires are clear of any moving parts of the loco. And also remember to remove the tape with which you taped down the decoder. Do all your programming and testing before replacing the loco shell - it's certainly a nuisance to have to take this loco's shell off again!
If anything about the procedure is perhaps still unclear, or if you used this guide and it worked for you, please drop me a note.
Good luck, and keep them on track!
The following pages contain decoder installation guides for some other N scale diesel locomotives:
And the following pages contain guides to servicing or performance enhancement of some N Scale diesel locomotives:
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Created in January 2001. Last updated on 11 September 2003.