3. Use a thin piece of metal to loosen the angular part at the left end of the chassis. Carefully lift the cover upward.
4. Remove the battery.
5. Drill a small hole for the wire into the battery chamber. 7-8 mm may fit. I made the hole in the battery hatch, but you can also place it elsewhere to allow the wire to connect to the battery contact plug.
6. Draw out the battery chamber. On its left side there is the battery contact plug with 4 legs. You will only use only the two outermost pins. Looking at the backside of the battery plus you can see two wires: a white (-) and a red (+). It is difficult to connect the wire from the power supply here. Use instead the pins at the inside, but note where the red wire is connected as this must receive + 7,5V.
7. Pull the cord through your hole in the battery chamber and solder the two wires to the outermost pins in the battery chamber. In most cases the positive wire from power supply will be marked with a white stripe in the black isolation. This wire must be soldered, so it connect to the red wire on the backside. If in doubt use a voltmeter to check.
8. Now assemble the battery chamber and its hatch in the chassis again in reverse order. Be careful to insert the small round pin, which functions as a shaft for the hatch.