Carefully open back plastic cover

Step 2
Time to set our trusty connector-seeking spudger loose to free the battery from its bonds.

The battery tray comes out, no problem.
Step 3
Opening cover of the battery power controller and taking solder iron in our hands with 2 wires, than solder it is as follows:

Step 4
Solder the wire to Hall Sensor (Take a soldering iron with a thin sting, put no more than 350 degrees Celsius)

1. Do not turn on the battery with turn off the display train. Otherwise, in the output, it will be a musical bricks.
2. Be careful with the glass.