Abs problems

My brakes stopped working properly in the wet the other day, the passenger side front wheel was juddering/locking up rapidly so when I got home I tryed lot pull any abs codes. The abs light just stayed on constant with the diagnostic terminals bridged and the wire in the drunk unplugged. The abs self checks and doesn't stay on normally though. I have read that this means the abs computer is malfunctioning, are there any other tests I need to do? If the computer needs to be replaced do I need one from the same year/rev? My car is a 1990 jap import sw20 NA
If I need to replace the computer does anyone have one that'll work?