The installation is for HO-Scale Hobbytown Baby Trainmaster. It uses T1 decoder and was performed by Jean Lacroix.
This model is a Hobbytown of Boston drive with a metal body shell from Bowser. On this model, the body is attached with screws located underneath the locomotive in the middle of it. Just removing the screws let the body free.
All the wires connected to the motor should be removed from it. The motor has to be unscrewed from its location since it would create an electrical short in dcc mode. To prevent that, install on the floor of the locomotive, where the motor was, a rubber pad or a piece of plastic large enough to isolate the motor from the frame.
The motor should be glued in place using Goo or silicone, taking care to avoid any moving parts. Pay special attention to align the drive shaft and the motor sprocket. Once you have soldered the wires on the motor terminals, add electrical tape over them in order to avoid contact with metal body that could create short circuit. You can use heat shrink tubing over each wires that are soldered together.
The orange and grey wire from the T1 harness should be soldered to the terminals located on both side of the motor.
Then connect the red wire to the top of the front truck and the black wire should be attached or soldered to the rear truck.
It is a good idea to add contact wires made of phosphor bronze, inserted in plastic tubing, on the side of truck that has insulated wheels.
The decoder can be installed on a plastic shelve sitting on top of the driveshaft or on the ceiling of the locomotive body using double sided tape.