Thanks! & 90 ABS problem?

[randrews@post.cis.smu.edu (Robert Paul Andrews)]

First lemme say thanks to all who helped me diagnose my fan problem with
my 88 90.  The fan itself had died :(  But now that major problem is out
of the way, I have a smaller one at hand.  Occasionally my Anti-lock off
light will come on when I hit a bump or jerk the car.  Any thoughts?  
It doesn't stay off long enough to test if the ABS is working, but I wouldn;t
even be sure on how to test the ABS.  Help please.  Thanks.
Rob
randrews@post.smu.edu