I have a 99 RANGER 3.0 4x4 I recently replaced the speed sensor and now its working but while driving around it goes out abs light comes on and o/d light blinks I cycle the key and it will start working again any idea what it can be ?

 

In a '99 Ranger the VSS signal from the rear axle sensor goes directly to the ABS module, it is corrected for axle ratio and tires size in that module, then sent to speedometer, computer(transmission) and cruise module.

So if ABS light comes on then problem is in the wiring from axle sensor to ABS module or ABS module itself.
Since cycling the key restores signal, ABS module or it's connector would be the prime suspect.

Not sure if there is a test for that module?
Ford Dealers can "talk" to these modules to change tire size in memory or axle ratio, so may be worth paying them for test, not sure what the cost is of a module.