before trying this, i'm assuming there is enough coolant your expansion tank to short the probes

The 2 pin plug that connects to the top of the expansion tank, disconnect it and short the 2 wires together. Start the engine, if the coolant light still flashes, i havent a clue, (clocks

) If it stops flashing, the electrical side is ok, and the problem is pointing to the probes. check the connections are clean on top of the probe assembly, and the plug.
Make sure the engine is cool, remove the expansion tank cap, then remove the probe assembly out the top of the expansion tank. clean the probes and refit.