I used to have a 94 Ranger 4 cyl with RABS and it had this light on off and on.
Here's what I learned.
First, the light on the dash is an idiot light that is thrown on by a number of issues, some of which are: brake fluid level, a problem in the ABS system. Look at a fuse box diagram and make sure you have fuses plugged in for ABS and that they are not blown.
As mentioned above, there is a fluid level sensor in the master cylinder. You will see the plug coming off the side of the plastic brake fluid reservoir. Is it connected? Try disconnecting the connector and cleaning the contacts with electronics cleaner, putting in di electric grease in there, and reconnecting.
Is the brake fluid topped off? Try that. Either of those two things may work.
If you have enough fluid and the connector and sensor seem good, then there are several other things to look at:
There is a sensor bolted into the top of the rear differential. Is it properly bolted in and is the electrical connector connected? Try cleaning that and reconnecting. This sensor is a magnetic pickup, basically, that reads a tone ring (toothed ring that looks like a gear) on the ring gear of the rear axle. It is trying to look for discrepancies between vehicle speed and the speed of the ring gear (i.e., brakes locked, vehicle sliding)
Next: As far as I know ALL RABS rangers up to 97 have one ABS hydraulic control unit on the drivers side frame rail, not far from where the fuel filter mounts (it is a brass machined block with two cylinders on top of it). It is possible for this unit to leak externally, which can cause a slow loss of fluid and or braking pressure and that threw on the ABS idiot light for me.
If this unit is leaking, it is usually pretty wet and obvious. A replacement is around $130 as I recall. The only way to bleed the new ABS unit would be to install it, then get a spare electrical connector for it, find power wire and ground wire from the new connector, and energize it from a spare battery with fluid in the master cyl reservoir, it would pump the valve unit and should purge air bubbles out to behind the new hydraulic unit, then you would have to bleed rear brakes as normal to bleed that air out of the system completely. There is a very expensive OBS ford tool to do this, some advanced scanners may be able to do it (Not a regular OBD2 scanner) but in theory the method I described would do it just fine.
EDIT: if you did not care about having RABS and your hydraulic unit is shot, then you can of course bypass it, would be as simple as fitting the inlet and outlet brake lines of thge ABS hydraulic unit to each other, and then bleeding the system again. If you do that, leave the electrical connector of the hydraulic unit connected or otherwise you will get the idiot light back. I did a bypass that way myself once, brakes worked great but could lock up since there was no ABS anymore, but the light did not come on since the unit was still plugged in.
I have 4 wheel ABS on my 96 Ranger and I absolutely love having it. When working, it is a wonderful safety feature and the truck stops great. The system really isn't that difficult to fix and is worth keeping if you want it. I have never had abs on a ford ranger cause an unsafe stopping condition... I have had gm ABS systems that felt like they wanted to kill me
Hopefully that covers it!! Update us with any progress