You need to check the alt amps output and the battery voltage while checking the amp output. That will tell you alot. If amps and volts are way to low then go to the field wire on the back of the alt that goes to the PCM and ground it to see if it gets full output. If it dont put out like that then check the voltages to the field wires and see if it has 12 or more on the 12 volt field wire. Ron