After removing the locomotive shell and rear weight, remove enough of the top of the rear weight the entire length for the decoder to fit in. There should be a ridge left on each side. This metal is not really hard and I do this with a hand file in about 15 minutes.
Next, file a slot up at an angle from the bottom front corner to the top at about 1/2 inch from the front. Then file a slot across the top to connect the angledslot with the area removed for the decoder. Do this on both sides. This will be the channels for the wires.
There are long wheel contact wipers that run the length of the plastic frame. You will need to remove all the existing connections to these.
The decoder and wires can be secured in place using a small amount of Wathers Goo.
The black, blue, & gray wires go to the left and the red, orange, & white wires go to the right. Re-install the rear weight and plastic retaining clip.
Connect the orange wire to the top motor contact and the gray wire to the bottom. Use a small piece of .010 styrene to insulate the contact strip from the motor connection.
Solder the red wire to the right contact strip and the black wire to the left contact strip.
The white and blue wires get run all the way to the front up under the front weight and up the slots to be connected to the light. In this example I had used the original light bulb but an LED could also be used with a resistor placed in series.
After checking all of the wires are clear of moving parts and that the flywheels are turning freely, the mechanism is ready to test run.