Kit: Zimo MX645 (hard-wired) with SugarCube9; 470uF stay-alive; yellow lamps at front and rear; SMD firebox glow LED; weathered crew

The donor loco and kit to fit...

A single screw opens the top off, revealing a reasonable amount of space in the boiler.

Fit a horizontal mount yellow lamp on the boiler door, and another one (for reverse motion) on the bunker

Make a hole for the firebox glow LED and a shallow channel for its' wires to run in, so they don't snag when the body/motor-back goes back into place later

A channel under the cab for the rear lamp's wires to run in

A resister for the firebox LED, one for the front lamp, and the rear lamp's resister was already in the bunker, protect with heat shrink and join ready for the common positive (blue) of the decoder

Shorten the purple speaker wires and stay-alive wires and attach the SugarCube9 and a 470uF electrolytic capacitor

Join up the common positive to the lamps/firebox wires, and join the function outputs (white for forward lamp, yellow for reverse lamp, and green for firebox glow).

Decoder goes sideways in the boiler, with capacitor at the front in the nose and speaker just behind. Pack speaker with a little Black Tack to stop it from moving freely and to reduce vibrations.

Connect pickups (red and black), then motor (orange and grey - swap around if it runs backwards!)

Grind a little edge off the front of the chassis, to avoid it cutting into the decoder, which just sits in that same space.

Tuck all wires neatly in and put the body back on. Weather up some crew, and carefully glue them through the open cab side - there does not appear to be any easy way to get into the cab on this model (strange design?) but through the cab side is possible with some care.

Final touch is to add some lump coal in the bunker to improve the appearance.

Please note that these guides are provided as useful resources for you, as-is. YouChoos cannot be held responsible for errors in the information, or for any damage caused to your models or equipment if you choose to follow any of the steps detailed here.