The level sensor (in the top of the left tank) is basically two prong
electrodes inserted into the coolant.  The sensor looks for a connection
across them.  If you are getting air (or other gas) into the system,
this will cause the sensor to blink.  If you have too much antifreeze
and not enough water in the mix, your light may blink (since antifreeze
does not conduct electricity well).  If you have a loose connector to
this sensor, it may blink.

It *should* blink for 5-10 seconds after you start the car -- this is a test.

Next time it starts blinking, immediately stop and check the coolant level in
the left tank (don't open it, though, it's pressurized).  If there's coolant
all the way to the top, check the connection.  If you put in too much 
antifreeze, and not enough water...

malcolm