This LED on a LC&D control panel is supposed to flash slowly when the clock is on the bus. In this case the LED will be mostly OFF with a Flash ON at about 1 time per second.
If it is flashing rapidly at about 10 times per second this means that everything is fine but it is storing data to nonvolatile memory so do not de-power the board.
If the LED is flashing slowly but is Mostly ON with a flash OFF this means that the board cannot see the clock (because it is disconnected) and that this board is “Mastering the Bus” (acting as the traffic cop for messages.) If the clock is connected then there is a problem. Either the clock is bad or the board has a bad communication chip.