I know a lot more about 2nd gen ABS. I could make up stuff and pretend it applies to a '93, and some of it will, but not necessarily all.
You should have front abs sensors in the wheel hubs, and rear, probably in the differential, mounted on the housing, then your ABS modulator has three lines out, to left and right front wheels, and one hydraulic line to the rear which splits at the left wheel and then the line goes across the rear axle to the right rear wheel, so same ABS circuit handles modulation for both rear wheels simultaneously.
These passive sensors produce a low voltage AC signal to the ABS controller, "Maybe". I mean it is low voltage AC but direct to the controller on a '93, IDK. Either way, you can measure for this low voltage while spinning the wheel, at the sensor pigtail connector. If you have a signal then check wire continuity between the mating connector and the ABS module, and that neither wire is shorted to ground from wiring damage.
A common cause of sensor dropout is a hub failing. If the sensor measures around a few hundred ohms (420 ohms or so for stock sensor on a 2nd gen front wheels, I don't recall the rear but would be between dozens and hundreds of ohms too) which indicates the inductive coil in it, and wire to it is intact, but no AC signal with the wheel spinning, then it is likely too large a gap or contaminated grease inside the hub from failing bearings.
If you are on your original hubs, it might be about due to have them replaced anyway and new hubs, usually come with new ABS sensors so you don't have to risk trying to remove the old ones, which often breaks them if there is any rust causing it to be stuck in the hub.
