The winding is achieved by an electric 12 volt motor at the rear of the movement. As the clock unwinds the weights drop lower and a trip arm attached to one of the weight's pulleys gradually pushes against a cam attached to a mechanical switch. This can be seen at the front of the movement as shown below.
Eventually when it is low enough the cam triggers a switch and the motor starts rewinding. As the weights then travel back upwards they will trip this mechanical switch again and switch the motor off when they get to the top.
Carl Bohmeier Master Clock
The picture above show the weights in their midway position as the clock is unwinding. I have highlighted the trip arm in red, and the edges of the switch's cam in blue. This cam is slowly pushed anti-clockwise on its pivot as the trip arm pushes it downwards. Eventually it gets top heavy and the cam flips over completely anti-clockwise, which operates the 'On' switch.
