It is supposed to blink at start up for a few seconds and then go out.
This tells you the system is working.  People say it will blink if your
antifreeze/water mix is off, but I'm not sure it is that smart.  When they
leak, it is usually at the electrodes.  It then pushes  up into the plug.
I've never seen one that leaks blink because the leakage simulates a full
tank.  I have seen gauges go bad and cause the blinking.

                                                        Jay