Ford Repair: ABS light on, speed sensors, abs brake

Question
I have a 1997 2WD Ford Explorer that is in excellent condition.  Recently the ABS brake light came on when I started the car and stayed on.  Then, the next time I started it, it did not come on.  I did numerous starting and stopping brake tests and everything seems fine.  Plenty of fluid, decently new pads and always routine maintenance.  Is there a reason it may have come on and then not came on again?  

Answer
The ABS light comes on when the computer sees a problem in the system, it resets when the vehicle is turned off.  The system doesn't have a memory and can't be properly diagnosed unless the light is on when testing.  When the light is on, the ABS will not work, but the vehicle is safe to drive.  I would guess the one of the Speed Sensors is going bad.

I hope this helps,
Dave