Parts required:

1 appropriate sound decoder (e.g. Soundtraxx DSD-090LC)
1 1/2-inch speaker to match sound decoder
1 Kato N scale Mikado
Soft, flexible wire - excess wire from the decoder should be enough.
2 sewing pins
Double-sided tape

Tools required:

Soldering iron and solder
Needlenose pliers
Needlenose tweezers
Jeweller's screwdrivers (phillips and flat head)
Sharp hobby knife
Electrical Tape

Instructions:

1) Separate the locomotive and tender. Lay the locomotive upside-down on the workbench, and lift the trailing wheels on the locomotive clear of the drawbar, by lining it up with the notch in the middle of the drawbar. Then pull the tender and locomotive apart. The drawbar should unclip from the locomotive. Leave the locomotive aside for the moment. Also, trim all of the decoder wires so that they are approximately 1 1/2 inch long, aside from the two speaker wires. Hold onto the excess wires - these will be used to connect the lights and motor.

2) Separate the top of the tender from the base. There is a post on the underside of the tender top. This will get in the way, so it will need to be removed. Also remove the plastic floor holding the weight bar in place. Take out the weight bar and trim it to match the length of the decoder - it will be going below the decoder once this is finished.

3) The next step is to remove the coal load. This is held in by two clips at the top of the tender, as shown below;

Once this has been done, there will be a flat area at the top of the tender, with two holes for the clips. Most of this area will need to be trimmed away to make room for the speaker, as shown below;

4) After this, the next step is to file a hole at the front of the tender to allow passage of the wires for the motor and headlights. This will need to be done on both the tender chassis;

and on the tender shell;

These should be wide enough to allow four wires through. The sound from the speaker will also escape through this gap, so I suggest you make it as wide as possible. If you are going to install a body-mounted Micro-Trains coupler (as I did), now is the time to do it.

5) Owing to the size of the decoder and speaker, the plastic floor clip removed earlier cannot be used. Due to the fact that this clip also holds down the tender power contacts, it will be necessary to slightly rebuild the tender power pickup system:

5.1) Remove the front tender truck, and remove the wheelsets. There should be two metal power pickups, one on each side of the truck. Remove both of them. You should have two items that look like this;

Apply a small amount of solder to each of these contacts, making sure that it does not go above the top of the truck sideframe. Once this has been done, re-insert the contacts into the plastic sideframe. Push a pin down through the top of the plastic sideframe, as shown below;

Once this has been done, trim the pin off approximately 1.2cm (1/2 inch) from the top of the plastic sideframe. Re-insert the wheelsets into the front truck, and reattach the front truck to the tender, making sure that the wires coming from the drawbar are inside the pins;

5.2) Solder a wire to the top of each of the contacts on the rear tender truck;

Once this has been done, solder the two wires from the rear truck to the corresponding pins on the front truck;

6) Glue the weight at the back of the tender, as shown below;

Once this has been done, use the double-sided tape to stick the decoder on top of the weight. Solder the power pickup wires from the decoder to the pins coming out of the bogies - red wire to the right hand side and black to the left hand:

Set the tender aside for the moment.

7) The next step is to disassemble the locomotive. Remove the handrails, then use two of the flat head jeweller's screwdrivers to push the cylinders away from the body slightly - just enough to release the smokebox. Wriggle the smokebox forward until it comes off the frame. Then lift the cab up - it should just unclip. The cab interior - this is a small piece with two seats cast into it - this should just slide backwards. The top of the boiler should just lift up off the locomotive at this point. The last pieces to remove are the running boards and firebox sides. These are the one assembly. To remove it, pull it away from the locomotive body at the firebox end. Then you will need to rotate it upwards, so that the section above the front driving wheels slips out from beneath the body. You shold be left with something that looks like this;

(Except the wires - these were the result of an earlier install)

8) Remove the light board by sliding it forwards. Cut the circuit board trace on both sides between the light and the contacts where it touches the chassis. Solder a wire to each side of the circuit board, taking note of which wire goes to which side. The left side needs to go to the white decoder wire, the right to the blue wire. As the lighting board uses a Light Emitting Diode, it is important to get the polarity correct.

9) Remove the clips holding the motor and worm gear in place (the dark grey plastic clips in the photo above). Loosen the two screws on the side of the mechanism, just enough to allow the motor to slip out. Lift the motor up and out of the locomotive. Use a flat-bladed jeweller's screwdriver to pry up the two motor caps, being careful not to lose the springs or brushes inside. Remove the contacts that touch the locomotive's frame. You should have two items that looks like this;

Using the excess wire from the decoder, solder the orange wire to the motor cap from the bottom of the motor, and the grey wire to the top cap. Once this has been done, re-assemble the motor, reversing the steps you used to dismantle it. Use the electrical tape to cover both caps. Make sure both caps and the ends of the wires are completely covered (this is the voice of experience speaking). Replace the motor inside the locomotive, running the orange wire through the gap between the two halves of the frame, as shown below;

Make sure that the wire does not interfere with the trailing truck. Grab the cab interior piece that you removed earlier and feed the orange wire through the rectangular slot in this part, before sliding it back into place. Then re-tighten the screws holding the two frame halves and replace the clips that hold the worm gear and motor.

10) To run the wires out of the locomotive body, you will need to drill three holes in the top of the firebox inside the cab;

Feed the wire from the top of the motor and the two light wires through these holes, replace the silver weight above the worm gear and headlight, and slip the boiler casing back onto the locomotive.

By now, you should have something that looks like this;

11) Re-connect the tender to the locomotive and solder the wires to the matching coloured wires from the decoder.

12) The only thing left to do is to install the speaker. You will not be able to use a speaker baffle, as there is not enough space. Follow the instructions that come with your decoder. Once you have connected the speaker, you will need to place it face-down at the front of the tender, then place the tender shell over the top, using the gap underneath the coal load to position the speaker and capacitor (if there is one);

Replace the coal load over the speaker. All that's left now is to program the locomotive and enjoy!

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