Decoder Installation into a
Mantua Mikado HO 2-8-2
For your information, I used a DH83FX decoder for this installation. I glued the decoder to the tab the motor was mounted to. If you want to stand the decoder up, you will need to use a shorter decoder. Or you can cut the excess shaft and let the decoder lean inside the cab. Of course, that excess shaft lends itself well to the addition of a counterweight. So you might want to put the decoder in the tender. Certainly, it will be out of sight here, but you will have 5 wires going between the locomotive and the tender instead of 3. Your choice. The primary purpose of my installation notes is to show where the wires go. Where you put the decoder is up to you. The wiring is the same no matter what.
This Mikado has a history to it. I got it when it was made by Tyco many years ago and had an open frame motor. As I recall, one side of the motor was attached to the frame - a DCC no no. Mantua once again manufacturers this locomotive and offers a can motor retrofit kit which I installed a few years ago.
Fortunately, the can motor is already electrically isolated from the frame. The existing headlight is attached to the frame. So replace it with a grain of wheat bulb. You will need to blacken the bulb wires - they will be noticable under the boiler if you don't.
Whenever possible, I prefer to run the appropriately colored DCC wire between the locomotive and tender. Yes, it shows, so you may want to blacken nearly all of it leave just a a touch a color somewhere underneath so it will be obvious what wire it is should you ever need to know. If you want to blacken it entirely, feel free.
Therefore, I found that when installing the rear headlight and splicing in the blue wire to the rear with the grain of wheat bulbs from the front, I didn't have a lot of slack. No big deal. To gain as much slack as possible, I ran the grain of wheat bulb wire along the locomotive frame and under the motor rather than over it. This is better, anyway, especially if you mount a flywheel on the back of the motor - you don't want it wearing away the insulation. So you will need to blacken the bulb wire nearly it's entire length. Then determine where to splice into the blue wire. Like I said, no big deal.
Connect the black wire to the tender. Connect the red wire to the locomotive frame - I suggest the screw for the gear head. Again, will need to blacken the red wire - it will be noticable under the boiler if you don't.
You might want to "tack" on the gray and orange wires until you are sure the locomotive will run the correct direction. Tack? Do what? This means a quick and dirty soldering job that's just good enough to hold the wires on. Whether or not you have to switch the wires, do a good soldering job once you have the right direction of travel.
When reassembling your locomotive, the screw going through the smoke stack will have a headlight wire pass on either side of it. Be mindful of this when you are screwing it back together! You may need to prespread the bulb wires a bit so the screw can get between the wires.
I drilled a small hole in the bottom of the tender for the rear headlight. I suggest sliding a small piece of heat shrink over these two wires and placing it through the hole to act as a wire strain relief.
Take all the decoder wires you have left over and cut the ends off of them so that there is no exposed wire. Put all of them inside a piece of heat shrink and shrink it. Do not solder them together! While cutting them flush almost guarantees that they will never short to anything, especially the frame (which is tied to one of the wire pick ups), almost doesn't count. You need a guarantee. If no heat shrink, then electrical tape - though electrical tape leaves a messy residue. If you are still thinking about not covering these ends, think of these two things: How much is that piece of heat shrink tubing worth? How much is a decoder worth?
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