I had to pull the alternator on the 99 and it has just under 60k
well the brushes were pretty worn, infact one was worn much more then the other.
so at high rpm the brushes will in a sense "hydroplane" or float and not actually make contact, I beleive this is what causes the battery light at high rpm, and that is why it is a sign of the alternator going
the brushes are spring loaded so after a certain point they will not make contact anymore, or the spring might weaken over time, thus not keeping contact
