the curse of the blue wire?

[Dave Aukerman]

Victim:  89 200tqw has developed a charge problem that came and went.  Took
alternator in to have rebuilt, only for the guy to ask why it was there, as
it worked fine.  Belt was brand new and tight.  Decided to drive it the
mechanic today and while running on battery power the car suddenly began
charging again.  I've examined the under hood connector for the bue wire.  A
bit of crud, but after cleaning and resnapping, the problem persisted.
Voltage was showing with the key in the on position.  What gives?

Dave