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![]() ![]() Don't leave it like that for long, or the voltage will fry things. That'd be one way to test if it's the altenator. Anyway, if I'm not totally off base on all this, then disconnecting the PCM wires and applying full voltage (12v or 5v, prefferably through a resistor cuz the transistor only needs the tiniest current to turn on) to it would make it go full-field(maximum output). Don't ask me for certain.that's what testing it is for. It's probably pulsed on and off quickly, and might only be running on 5 volts(again, test for it). The wire to it is the one I'd be most interested in checking.that looks like it should be an NPN transistor, meaning there should be positive voltage coming in from the PCM there(test for it, #2 wire/connector). At a guess, either it's not getting turned on (often) enough or it's overheating/faulty. If i'm reading it right, it looks like the transistor in the altenator controls the field coil. 'course, it might be all over the place as the PCM makes adjustments. Well, you could check the voltage at the wires that go to the PCM, first when the alternator is working properly and then again when it's not.the theory being that if they read the same before as they do after, then the problem is in the alternator. I'd just replace the alternator, but it's $200, and the PCM is $300. I checked all those fuses, too, all fine. Here's the official Mazda wiring diagram for the charging circuit: ![]() I cannot find anywhere how to test the PCM output to rule out the PCM as a possibility, the factory service manual is a complete piece of crap, as is the wiring supplement. The weird part is, the voltage regulator isn't in the alternator, it's controlled by the PCM.
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