If you have a multimeter, put it on continuity check mode, and see how the wires relate to the bulb sockets. If I were to guess (and mind you, I am) it looks like either power or ground is common to all of the bulb sockets, and the remaining wires are connected in banks to the other side of the sockets to form a 3-step marquee lighting animation. If this is the case, there was surely a control board which did the switching to achieve this.