This circuit is designed to flash two sets of 12 LEDs on and off to signal the raising or lowering of a lift bridge.

The LEDs are wired alternatively so that every other light is illuminated together.  A potentiometer on the board alters the flash rate and a pair of wires are connected together to start the flashing.

The circuit board contains a microcontroller (lower left), a voltage regulator (upper right) and two large power transistors (top center and top left).  The flash rate adjustment is by way of the potentiometer in the lower left.  The white/yellow wires start the flashing when they are connected together.  The three wires in the upper left (red/white/black) go to the LEDs.  Power is supplied through the wires in the upper right (red/black).  Voltage should be between 7 and 12 volts.  Since the LEDs are directly powered by the input voltage care should be taken not to exceed 12 volts DC.