what would cause a 2000 ford exped eb to just lose power after alternator been replaced

my guess is u had a big amp installed with this sterio maybe even two or more smaller amps? if so your probly overloading your altternator . you need to add up your amp draw for all asserys running at once.including rear defoster ,a/c, hadlights once you know how many amps you are drawing totol the alt will have a raiting to on its tag,your totol number should never be more than 75% of what your alt is raited for. if ya cant figure all that ouy just add anouther battery and a capasitor ya should do just fine then

no amp or anything just a new head unit

Make sure that the correct alternator was installed. My father drove a car around for about a year with goofy lights flickering and flashing. We could never figure out what was wrong. Eventually we learned that the autoparts store had sold us the wrong alternator.