My 96 cavalier, showed engine light was running fine. it lost all power so put a rebuilt alternator in it and it ran for two more days fine. lost everything again,had alternator and battery checked,everything ok. car stll does same thing....HELP

Need to do a battery draw test. remove the negative cable from the battery, and clip a test light to each connection of this cable and battery. with the key out of the ignition there should not be a light on in the test light, if there is, remove the fuses one by one to find the circuit that is draining the battery. also keep in mind that an over charging altinator can give this symptom. the altinator should be as follows.
no less than 12volt
and no more than 14.5 volt. any higher can over charge the battery and fry it out, as well as give too much voltage to the computer of the vehicle. if none of this applies, then there is a wiring problem.