I cant believe a ten year old thread has been reopened so many times.
I didn't even know DF was around in 2003.
maybe this should be moved to the WTF thread.
There are several things to check
First type "ABS light" in the search box, but put it in quotes like I did. This will bring up tons of threads on this subject.
In short order the most common causes.
Speed sensor on Rear diff, (don't use aftermarket sensors)
brake line from front to back (inside frame rail above gas tank)
front ABS sensors (if you have 4 wheel ABS)
There are a couple more but these are the first ones to check.
Welcome to DF