[shorod]

A standard scan tool will not work with the ABS system, it needs to be either a specific scan tool for the brakes or a professional grade scan tool.

The issues you describe really could be due to any of the items you note, however I don't think a faulty brake fluid level sensor would cause the ABS to not work. My guess would be either a wheel speed sensor or a problem with the Hydraulic Control Unit. I'm not totally sure of the specifics for your 2001 model year Taurus, but usually the system will perform a self test after the car is started. That may explain why sometimes the light does not come on right away after you start the engine. And the problem could be as simple as a weak charging system or a loose/dirty connection.

The easiest way to diagnose this would be to get an ABS scan tool and see what direction the codes point you.

As for changing bulbs in the instrument cluster, sorry, you need to pull the cluster. The good news is that's not all that difficult, at least not when you hands are warm.

-Rod