The GEM module is spliced into the 2 wires from the rear ABS sensor, and GEM module uses that 25,000ppm speed pulse, and converts it to the 8,000ppm pulse that Ford uses for speedometers, computers and cruise control
So without that pulse speedometer would be incorrect or not working at all
In a 1999 Ranger there would also be a code, P0500 and CEL(check engine light) would come on
So ABS light is an issue with the ABS module, its rear axle sensor circuit
Could just be dirty connection, unplug module's connector and plug it back in, that cleans the contacts at the module
See of the code comes back
This rear axle ABS sensor generates its own AC voltage when rear axles are spinning, so doesn't require voltage from the ABS module or GEM module
Called a Variable Reluctance(VR) sensor
Most ABS sensors are VR type as are most RPM sensors, in engines and transmissions
You can try changing it, it is possible an incorrect signal effects ABS module but not GEM