What can turn on the battery light in the car other than the battery and alternator?

My car is a 96 ford contour. The car was perfectly fine when all of a sudden the battery light on dash started to flicker. When we parked the car at home and attempted to turn back on the car wouldn t start. Tried it again nexed day and at the first try car turned on but battery light remained on. When turned off and attempted to turn on again car wouldnt start. We went and checked the alternator and were told that regulator wasn't working. So we changed the whole alternator (just in case). We checked the battery and were told battery wasn't holding charge. So we bought a new one. Battery light is still on. We cleaned all possible corrosion in wires on alternator and battery but still light is on. We're at a stand still any ideas of what else we can check?

Connect an obdII reader and delete the error code to switch off the light

After changing the alternator did you test the new one? Kind of important to know if you got a defective new part.

Confirm if your alternator is good. Get a multimeter, start engine let idle for a minute and rev to 1500 rpm. Set the multimeter to read DC voltage. Measure the voltage across the battery. Under 13.6 volts and you have a bad alternator, bad wiring/terminals, bad ground or fuses.