Source google image: http://upload.wikimedia.org/wikipedia/commons/thumb/2/21/Trolleybus_diagram-key.svg/440px-Trolleybus_diagram-key.svg.png
Schema electrique d un bus
Source google image: http://upload.wikimedia.org/wikipedia/commons/thumb/2/21/Trolleybus_diagram-key.svg/440px-Trolleybus_diagram-key.svg.png