Pull the connector from the brake fluid level sensor. Then turn ignition on, the brake fluid warning should now appear, also you will see the (!) symbol light up... Now short out the two contacts in the connector (obviously the part with the cable attached, not on the sensor) - the light should go off. If it does the level sensor is broken, if it still is light up this would indicate a wiring issue, or an internal fault in the speedo cluster. This can also be tested, just check with shorting first and post result.