Are you sure that one of the wires on the high out on the crossover
hasn't come undone?, or that one of the wires on the back if the
tweeter didn't come unsoldered?
the reason i bring this up is because i too have the MB Quart 6.5"
component sets,
and the crossovers have two sets of inputs +/-l&r high input,+/-l&r low
input on the crossover, and one of the wires has worked itself loose on
one of my tweeters before and i've had to resolder it before.
check it out, it maybe simple.