I replaced my Delco 10-DN alternator with a remanufactured one recently since the bearing was shot and making a lot of noise. I have an old mechanical Delco voltage regulator on the firewall. 12V system. Battery is good and fully charged.
The "new" alternator charges correctly; goes up to 10 amps then tapers down to zero as it should. However, once the engine goes to idle, it registers a 10 amp
discharge and stays there at idle until I hit the throttle again, when it then charges and tapers back to zero, as long as I am throttled up. I do not get a discharge when the engine is off and ignition switch is off, so I surmise that there is no voltage loss other than in the charging circuit.
Perhaps the remanufactured unit has some diodes burned out?? Or might a bad regulator be the culprit?
The old alternator did not do this and I did not change the wiring (2-wire setup, I think, no idiot light).