The original wiring. Carefully remove the motor brush caps slowly to prevent the spring from jumping out. Desolder the vertical copper strips from the left hand end in this photo - put a screwdriver blade behind one strip, appply heat to the blob of solder and use the blade to spring the strip away.

Unscrew the screw which provides a connection between the left wheels and the chassis. Lift off the circuit board.

Unsolder and remove completely the capacitor (under the board) and the choke coil. It is unlikely that these will come off easily. You wont be re-using them though. Clean up the soldered contacts and apply a new blob of solder to the front two joints where the pickup strips will be connected.

Re-secure the circuit board, and re-solder the two copper pickup strips. You may need to hold the strip down as the solder cools. The black lead needs to be re-soldered to the right hand (far side in the picture) joint. Be prepared for the pickup strip to spring free !