On Ford trucks the alternator itself is self contained BUT the PCM actually controls the internal regulator. It turns it on/off as needed to charge the battery. The first thing I would do is check every connection, a loose wire or even a corroded pin can be enough to stop the system from operating properly. If it discharged the battery I would suspect the replacement unit has a bad diode in it. Easy test. Disconnect the battery cable from the back of the alternator, with the key off and everything shut off, connect a test light in between the cable and terminal. If the light comes on, you have a problem as current is flowing in a system that should be off.
Thursday, April 27th, 2017 AT 11:12 PM