A few weeks ago my truck's Anti-Lock light stayed on.  Never happened before, but over the past few weeks it started coming on more and more frequently.  I suspected that I had done something to it when I was under the front replacing the shock mounts this summer. 

I finally got under there yesterday, cleaned the area up a bit, then traced the ABS wire down and to the caliper to make sure it wasn't being pulled on by anything, then I just pressed it down into the caliper.  I did this on both front wheels, everything looked clean and normal.  But I did feel a slight click on one of the wires as I pushed it in -- so slight that I really thought I had just pushed the cover of the wire around a bit.  However, in the last 5 driving cycles the light has gone off exactly how it should. 

Lesson = be careful with those wires when you work on the suspension.  And it seems to be true that just a slight separation of the sensor from the wire or the housing will cause the system to read it as a fault.