94 Taurus Antilock brake light

Hi all. I have a 94 Taurus GL 3.8 L engine. ABS 4 wheel disc brakes. (210,000 kms)
5 months ago I replaced all the pads (all for wheels) and the rear passenger
caliper because it was seized. Last week, my Antilock brake light came on & now stays on. Does any body know any any backyard fault finding styles that I could use to identify what part of my brakes is causing the light to stay on or is this strictly a dealer/professional mechanic area? There are no leaks that I can see, (no signs of drips/wet spots anyway), and the car brakes stop me with no apparent problems.
Any ideas would be greatly appreciated.
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