Hi,
In my experience of this ABS system if you have an amber light on the dash and you are able to put it out it by switching the ignition off and then back on again then it is usually a wheel sensor related problem.
If however the light stays on permanently with ignition on, it is usually something within the system itself. Quite a common problem (I would check first) is a lack of normal battery voltage (NBV) at Pin 2 of the ABS ECM, this can sometimes be caused by a bad connection when aftermarket alarm/immobilliser's have been fitted around the normal supply from the ignition switch and sometimes the wiring gets disturbed.

CheeRS, Mike.