Does the ABS light come on at all. It should be on if you turn the key to the on position. If it doesn't light then, I would check the fuse. Normally, the ABS light will light if there is a problem with a sensor, but that isn't carved in stone. The bulb could also be bad! I do know that the system that Ford dealerships use(can't remember what it is right now), can test all of the sensors and tell you which one is bad, or giving no reading. I don't know if the systems that other shops have will do that or not, but they should. I do know that my 93 Ranger has a bad sensor for the rear, and those brakes will lock up easy. The light is also on on the dash(under the black tape).
One thing about ABS. They are designed to operate as regular brakes, if the ABS system is not operating properly. They will stop you, but as you found out, they will lock up and slide.
