Now reassembly. Put on the black part with the electronics, take care of the red button from the switch that it is in right position. I had a little trouble with it because teh red button always fell down or the black rolls falled away. That was something ugly to work. ...Then drill in all scres.

Okay, there are the two preassembeled wheels with wires.

It only fits in ONE postion, there is a notch and then it snaps in.

Just snap it in, look where is upside and then it is really easy. The wires of the batteriecase have to look upwards.