93 F250 ABS light flashing

I have a 1993 F250 w/351 gas the ABS light in the dash is flashing. I have put fluid in it. It stopped for about 20 minutes & then started back. It flashes 15 times & then goes solid for about 3 seconds. Can anyone help? Thanks

Have you checked the fuse to the abs controller? The first step in that test is to confirm the fuse is good.