My alternator is not putting out adequate voltage with the car running. Is this

What is your question?

The battery voltage is 12.4v The output from the alternator with the car running is 11.5v. There are no positive or negative circuit voltage drops. There is no voltage in the gray wire or gray/red wire of the 2 wire connector to the alternator. Should there be constant power in the gray wire even when the car is off? Is this a gray wire problem or a bad alternator?

What makes this problem better or worse?

Constant problem

How long has your 1999 Mazda Miata had this problem?

a few days