My son's MPV had what seemed to be an alternator problen about 6-8 weeks ago. Pulled it off and tested it---all ok. Re-installed and everything worked fine. We figured there was probably just a loose connection in the wiring, which was inadvertently corrected during the task. Now it has done it again. Same results, pulled the alternator and took it to the BIG auto parts chain store. Ran the tests on the machine twice, passed both times. While re-installing it I did find a loose connector on the main wire which I repaired , thinking oh boy, I found the problem. Well, not so. Still no charge, and the bat indicator light is on. We checked the two wire plug on the rear of the alternator with a digital voltmeter. One wire is at battery voltage at all times(12.40 V), and the other is approx 1-1.5 V less (11.09V if I recall correctly) when the ignition is in the run position. Is the voltage reading correct on the "switched" wire, or do I need to look at this circuit for the problem?

 

i dont know mazda.
but on my volvo, you can find 3 wires off the alt.
1 is the ground and another is the primary charging circuit (thicker wire). the 3rd is 1 that feeds a signal to the battery idiot light. on mine, that 3rd wire became severed. what that meant for my volvo is that the car would run, but the battery would not charge (stuck at 12 volt). you need to "excite" the alt to get it to start charging (13-14 volts). the alt needs a "jump" of sorts which is supplied by that 3rd wire. if you were to rev the engine to, like, 5k rpm, a good alt will then "self-excite" and begin charging again.
.... but this is all on a volvo 240. not a mazda... but most cars are some what similar.