Parts stores would pull codes only, they do not do live data. The wires on the alternator really do nothing on this car, just turn it on/off and carry the charge back to the battery. The ECM has the voltage sensing inside it and reads the voltage through its battery feed.
On other systems the light is actually connected to the alternator and goes off when the voltage out of the alternator rises higher than battery voltage. In your case the light is turned on/off by the ECM when it sees the alternator changing the system voltage to above battery voltage.
The battery terminal outputs to the fuse box and starter and battery. Also it needs a good ground. So you would check the negative battery cable connections and the engine to body ground connection. Then the alternator battery feed to its connection on the starter and battery as well as the connection to the fuse panel. If those are all clean and tight, then it could be the connection on the ECM itself that is loose or corroded.
Thursday, August 2nd, 2018 AT 9:26 AM